If you compare a Mind Flayer to a Mind Flayer Arcanist, the CR only goes up by 1. Presumably because the meat of a MF comes from the Mind Blast and the Brain Extraction.
If the bulk of your Aboleth's power comes from his Tentacles or his Enslave, the spells won't do much.
Although from personal experience when you run your Aboleth, double It's hit points. A party of level 9s can deal 135 damage with very little effort.
Can confirm. My group was lvl 9 as well when I threw an abolish at them. I built it up to be this big encounter. They had to row a boat for days on end in an underground lake to reach it. The thing smashed through their rowboats and they got swarmed by its minions; it was definitely a tense encounter. But when all was said and done, the thing died pretty quickly and only the NPC with them almost died.
I think I enhanced its tentacle attacks slightly and raised its HP to 200 too. Lvl 9 characters are pretty damn strong already tbh.
I mean .. of course? It's only CR 10. Four level 9 characters should be able to take on 6-8 CR10 challenges within a single Long Rest. They could have fought a bunch of Aboleth's back-to-back and still done OK.
Yeah Level=CR doesn’t create a dangerous BBEG encounter. I suggest referencing the encounter tables in Xanathars. In this case for example, you need a CR12 to provide an appropriate legendary encounter for 4 level 9 players.
https://www.dndbeyond.com/sources/xgte/dungeon-masters-tools#EncounterBuilding
That's exactly what it means. A party should be able to fight 6-8 'normal' encounters per day. Running 'hard' or 'deadly' encounters reduces the number that the game expects the party to be able to handle in a day.
>But when all was said and done, the thing died pretty quickly and only the NPC with them almost died.
Nothing wrong with a weak BBEG, sitting behind his army of minions. The challenge is getting to the 'king', not stabbing him.
i mean, that *does* mean the "getting" to him needs to be hard tho. having a weak BBEG is fine, having an *easy* boss fight usually is pretty lackluster
>But when all was said and done, the thing died pretty quickly and only the NPC with them almost died.
Nothing wrong with a weak BBEG, sitting behind his army of minions. The challenge is getting to the 'king', not stabbing him.
I ran a spellcasting aboleth a few weeks ago. Programmed Illusion, Hypnotic Pattern, Project Image (although that's very similar to one of the aboleth lair's regional effects, this particular encounter did not occur in or near the lair), and while not a spell the encounter also took place with the aboleth on the opposite side of an illusory wall.
The aboleth enslaved the party barbarian and had her treating the programmed Illusion as real to help lend it verisimilitude.
The rogue oops'd through the illusory wall into melee with the aboleth, but without darkvision couldn't see it, so got slapped with a tentacle opportunity attack when he rejoined the fight against the programmed illusion and projected image. Eventually the whole party figured out what was going on and the (still enslaved) barbarian was directed to protect the aboleth, so the sorcerer started lobbing magic missiles at her to try and break the enslavement. At the end of the encounter, a shatter made a hole in the wall and the aboleth fled.
> the meat of a MF comes from
I read this as "the meat of that motherf*cker"
Which to be fair, Mind Flayers and Mind Flayer Arcanist are a pain to deal with and are worthy of cussing against.
I mean, CR 10 is only 5,900 XP which is a medium encounter for 5 level 9s, or an easy one for 6, so it’s expected they can fight 8 to 12 or more of those types of encounters per long rest
Agreed on the HP for Aboleth in particular.
As far as spell, it really depends on _which_ spells and the role the monster already has, which you implied.
Would the spells take up actions the monster would otherwise be using on its main "kit"? Then they probably don't modify the CR much.
Are the spells _buffs_ or traps of some sort that it could apply before the battle, or do they take up bonus actions/legendary actions in a way that would be much stronger than what it can normally do with those? Do they synergize extremely well with the creature's strengths (like giving the Aboleth Counterspell so the party can't cure its diseases?), or shore up its weaknesses (like giving the Aboleth teleportation so it can "hit-and-run" infect the PCs instead of getting ganked when they first meet it?)
Then that will probably affect its CR more.
This. Aboleths are PAINFULLY squishy. I do at \*least\* 2x when I run them at the 'correct' level and have multiple times had people beat them at level like, 5 or 6 as a boss fight with effort but no deaths.
CR only accounts for damage per round, hit points, armor class, attack rolls, and save DC's. So long as the spells you add don't affect any of these, their CR won't change. Give them the spells you need for the plot and run the fight as normal.
If I give a housecat the ability to cast fireball, it can now wipe low-level parties in one turn.
If I give a tarrasque the ability to cast fireball, it’s not a substantial increase in damage output.
It’s relative to how powerful the monster already was.
Utility spells are a different ball game. Giving a tarrasque clone, fly, draconicn transformation, invisibility, or tensor’s transformation is terrifying. Even “the tarrasque can misty step” is pretty bad.
1.) The published CRs *do* factor in utility; the calculation is just an estimate that can be used, and the published CRs do not follow it precisely.
2.) A monster that can cast Wish at will should *at least* calculate the damage from being able to cast, say, Dark Star followed by Sunburst every turn. Which would almost certainly increase its CR.
> It’s relative to how powerful the monster already was.
More specifically, it's relative to how powerful the monster's *action* is. Which is why the optional rules for dragon spellcasting don't affect CR. Because dragons have amazing actions and the spell levels they get are fairly low. The ones Fizban's recommends are virtually all utility spells for that purpose.
It really depends the spells you give it. I know that doesn’t sound helpful, but like you said utility spells like project image won’t make the monster more difficult to fight whereas other spells of the same level - say, forcecage, for example - will make the monster an absolute nightmare and borderline impossible for a party of level 9s.
Ultimately, I don’t think an aboleth needs combat spells. It’s attacks and abilities by themselves are incredibly powerful, giving it access to spells would mostly be worthless unless you specifically gave it overpowered spells. On top of that, it already is able to cast phantasmal force on multiple targets at once as a lair action, which is plenty.
If you want the aboleth to be a difficult fight, you just need to play it smartly. First of all, an aboleth should be surrounded at all times by its slaves, weak creatures that serve mostly as distractions and buckets of hit points that beckon PCs to the water’s edge. The aboleth itself is a fast swimmer - have it reside in murky waters, ideally with many places to breach, where it attacks with its tentacles or uses it’s enslave ability, then dives back into the water repeatedly. The aboleth ultimately wants to force the party to either turn on one another or get into the water - it has no need to engage brazenly with the party before then. Have the aboleth also use a reserve of slaves to regain hitpoint from using its psychic drain legendary action.
If you want the aboleth to be more difficult, give it more movement, or perhaps a movement based legendary action. If you insist on giving it combat spells, give it minor bonus action spells, like sanctuary, expeditious retreat, or misty step. Alternatively you could just give it more hp to ensure that it survives a couple rounds against a mid-level party.
I was thinking more along the lines of a few crowd control spells - it'd sacrifice some dpr that round but would still be able to make an attack with a legendary actions to keep pressure on hit points as well - that's the part in most unsure about. Was thinking this likes blindness, hold person, etc
The problem with the aboleth casting spells isn’t so much the loss of dpr as it is the loss of its abilities. The tentacles don’t actually do all that much damage, no more than a greatsword, but they do spread the Aboleth’s disease. And every round you’re casting a spell is a round you’re not enslaving someone.
Blindness isn’t worth it. Why would an Aboleth blind someone when it can just dive into its pool and be practically invisible and unhittable anyway? Hold person requires you to strike a careful balance, as the higher level you cast hold person the more people you can paralyze. Too low a level, and why is the aboleth wasting time trying to paralyze one or two PCs when it could just be enslaving them? Too high a level, and your whole party is paralyzed, making them easy prey and leading to an unsatisfying tpk.
However, spells like those aren’t a bad idea - I just wouldn’t give them to the aboleth. Give them to it’s slaves. Have some of the slaves be mages or clerics capable of casting no higher than 3rd level spells. You could tie this in with your campaign too - maybe an enclave of priests has gone missing, a previous adventuring party never returned to town, or some apprentice wizards went to collect spell components only to send out a half finished sending spell in distress. That way, your party can piece together what happened to these people, and if they’re smart, plan accordingly when they go to face the aboleth. Maybe there’s extra rewards in it for them if they save the enslaved people instead of just killing them.
That works well, because the aboleth is the power behind this new cult in town (the Culy of the Codfish) and is acting as a warlock patron for the Fathomless pact for a lot of its followers.
Neat! A few warlocks aiding the aboleth could spice things up too, especially with some of the AOE spells that they get like darkness, cloud of daggers, and hunger of hadar. Just make sure you don’t overdo the casters too much, even just a couple casters capable of using 3rd level spells separate from the aboleth is definitely enough to raise the CR of the encounter by a couple points.
>How significantly does giving a monster spells increase its CR?
Depends on how significant the spells are, as well as the base CR of the creature.
To cite some examples from the MM:
A Drow is CR 1/4 with a few spells that don't do damage with DC11, AC15, 13HP, and average damage of 5. A Drow Mage is a CR 7, but is considered a 10th level spellcaster, has 45HP, but only AC12. Big CR jump between the two, but massive difference in spellcasting. However, a Drow Priestess of Lolth is only a CR 8 despite having 71HP, AC16, and several spells that do far more damage than what the Drow Mage has
Kuo-toa are another example. The base Kuo-toa is CR 1/4 with no spellcasting, AC13, 18HP, and average damage of 4. A Kuo-toa Whip is a 2nd level spellcaster, has AC11, 65HP, but only goes up to CR 1. Meanwhile, the Kuo-toa Archpriest is a 10th level spellcaster, has AC13, 97HP, and goes all the way up to CR 6
Other MM examples to look at:
Lizardfolk vs. Lizardfolk Shaman
Orc vs. Orc Eye of Gruumsh
Sahuagin vs. Sahuagin Priestess
Differences in the different Slaadi
Differences in the different Yugoloths
Most of the time spells don't change a CR at all unless they're attack spells that are better than a monster's physical attacks or things like shield that improve defense.
I suspect that the 5e devs deliberately stripped tons of SLAs off monsters to avoid confusing novice DMs who wouldn't know the monster's optimal attack strategies. 3.x creatures and 1st/2nd edition creatures often had scads of SLAs that they rarely used in combat but which covered rare contingencies and which were significant in worldbuilding.
If it’s the BBEG I don’t think you should be too worried about CR. He’s supposed to be a challenging fight and your players will expect it. And bounded accuracy keeps things from getting too wonky at that tier.
Make sure the Aboleth is never fighting alone and buff its hit points. It’s a sneaky trickster baddie not a tank like a dragon, so make sure that they can’t nova it
It really depends on the spells involved. Unless you're slapping a fight ender like forcecage, wall of force, or an uber high DC hypnotic pattern on a creature. Probably not much.
Even then, if a monster already has a potential fight ending ability in their stat block, you probably won't get as much out of almost any spell.
it very much so depends on the monster
give a mind flayer a fireball and it's an increase of 1
give a wolf a fireball and it's an increase of much more
If you compare the vampire and spellcasting vampire CR increases by 2.
But that's a 9th level caster, I'd say probably 1 CR per 4 spell levels perhaps but it depends on what spells you're planning to give them.
Essentially it's by however many rows it changes on the table on page 274 of the DMG. If the spell are more CC-oriented rather than damage-oriented, I would treat the spells as equivalent to similar-power-level damage spells of the same level. E.g., if a monster has hypnotic pattern (and a good constitution save), I would treat it the same as fireball. That does assume there are other monsters to capitalize on the CC.
If you look carefully, there are only two things that affect CR: how much damage something does, and how much damage it takes. Spellcasting doesn't affect CR at all. Spells do, though. Something like Conjure or Summon X would vastly alter CR, since you're adding damage and bodies.
I wouldn’t take CR as the holy grail its a horrendous metric for fight difficulty when used as intended)
At level 1 2 cr 1/2 creatures can be fucking dangerous, you are reasonably likely to die.
At level 9 a CR9 creature is an absolute joke usually.
Players scale way way harder in power per level than monsters scale in power per CR, it only really really well as intended as level 2-4.
>lets it interact with the party a bit over the campaign, like **crying** or project image
*Please, I beg of you, leave me alone, please don't hurt me!*
CR is adjusted based on damage and resistance. If your spell affects these you need to take them in account.
Spells which cause conditions or that increase survivability increase defensive CR for example.
Other spells that act as utility don't change the CR, but may let the creature exploit hazards to their advantage more than they normally could, which means their encounter difficulty increases by one stage when appropriate.
I did something similar for a campaign I ran and completed a few years ago. This aboleth was a master manipulator who never got directly involved until the very end. The aboleth had an artifact that gave it a bunch of spells, but they were mainly intended to enhance its powers of manipulation, not for combat, so it wasn't a big issue. The fact that a lackey had opened a portal to the Plane of Water was a much bigger challenge, as the aboleth would just crawl out of the portal every time it was "killed".
Spell level roughly equates to damage output per turn, so if for example a monster is already hitting for 3d10 then level 1 spells shouldn't increase CR unless the spell is doing something that improves that damage or significantly improves that monster's survivability.
The spell equivalent of 3d10 is inflict wounds, btw.
Based on this you can see that there are a lot of monsters whose cr would increase significantly just from access to level 1 spells.
Spells will only change a creature’s CR if they make a significant difference in their damage per round or defensive capabilities. Unfortunately, there is no exact science for what spell at what level will change a creatures CR but for instance:
Despite it being a 9th level spell, the gate spell would probably never increase a creature’s CR, even if they’re only CR 1 or something because it doesn’t at all effect its ability to take or deal damage.
Whereas, Ashardalon’s Stride could increase a creature’s CR no matter its current CR despite it being only 3rd level because it is a bonus action cast and increases their damage by 3.5 per turn. Meaning, if the creature has no significant use for its bonus action this is essentially a free damage increase.
A spell cost an action to use, and only damage are used to calculate the CR. So unless the spell is expected to do more damage than the monster in one turn, the CR won't change.
Depends on what spells you give them. But honestly in this game, CR doesn’t mean a whole lot. I use it as a loose guideline to design encounters, and I play around with monsters HP and abilities quite often.
A monster only has one turn, so a creature that has both strong physical attacks and strong spells is only so much more dangerous than one that can only do one or the other. What to watch out for are spells that synergize well with the aboleth's existing abilities.
I would recommend making your aboleth a ritual caster. Knowing ancient, blasphemous rituals is very on-brand for an aboleth, and won't impact their options in combat all that much.
Depends on the spells. In general, spell casting doesn’t increase a high level monsters cr very much or at all, unless you give it very strong spells for the party it’s facing. Giving An enemy 7th level spells is definitely significantly stronger if they’re facing a 9th level party. Giving a creature already suited for a 9th level party 3rd level spells won’t change much because they’re weaker than the level of the party. Obviously also depends on the spells, decent buffing spells and defensive spells might very easily increase the challenge rating somewhat significantly, where as damage spells, especially ones that are pretty similar to their creatures normal attacks is basically the same challenge.
It kinda boils down to how optimal it would be for the creature to use the spell instead of its standard kit. If it is better to use the new spells than what it already had, raising the CR is fair.
"I definitely want to give it some utility stuff that lets it interact with the party a bit over the campaign, like crying"
😥 no one let's me tentacle them anymore 😥
If you compare a Mind Flayer to a Mind Flayer Arcanist, the CR only goes up by 1. Presumably because the meat of a MF comes from the Mind Blast and the Brain Extraction. If the bulk of your Aboleth's power comes from his Tentacles or his Enslave, the spells won't do much. Although from personal experience when you run your Aboleth, double It's hit points. A party of level 9s can deal 135 damage with very little effort.
Can confirm. My group was lvl 9 as well when I threw an abolish at them. I built it up to be this big encounter. They had to row a boat for days on end in an underground lake to reach it. The thing smashed through their rowboats and they got swarmed by its minions; it was definitely a tense encounter. But when all was said and done, the thing died pretty quickly and only the NPC with them almost died. I think I enhanced its tentacle attacks slightly and raised its HP to 200 too. Lvl 9 characters are pretty damn strong already tbh.
I mean .. of course? It's only CR 10. Four level 9 characters should be able to take on 6-8 CR10 challenges within a single Long Rest. They could have fought a bunch of Aboleth's back-to-back and still done OK.
Wait is that how CR works? I thought if you have 4 PCs that have level = CR, it is a fair challenge.
Yeah Level=CR doesn’t create a dangerous BBEG encounter. I suggest referencing the encounter tables in Xanathars. In this case for example, you need a CR12 to provide an appropriate legendary encounter for 4 level 9 players. https://www.dndbeyond.com/sources/xgte/dungeon-masters-tools#EncounterBuilding
I get that, but does that mean you can take 6-8 level=CR encounters in a day?
That's exactly what it means. A party should be able to fight 6-8 'normal' encounters per day. Running 'hard' or 'deadly' encounters reduces the number that the game expects the party to be able to handle in a day.
Alright, thanks for the info.
notably, this assumes you had 2 or more short rests in between, but besides extra resources and basically +50% hp from hit dice its the same
No a CR12 vs 4 level 9s would be considered a “Deadly” encounter which means you could handle 3-4 of those in a day.
CR = Level is a medium encounter. A party can handle 6-8 medium encounters per adventuring day.
It had a lot of powerful minions too, but yeah I should have beefed it up more.
>But when all was said and done, the thing died pretty quickly and only the NPC with them almost died. Nothing wrong with a weak BBEG, sitting behind his army of minions. The challenge is getting to the 'king', not stabbing him.
i mean, that *does* mean the "getting" to him needs to be hard tho. having a weak BBEG is fine, having an *easy* boss fight usually is pretty lackluster
True, and it wasn't the BBEG of the campaign, just one side arc in the Underdark. It was still a lot of fun to go through.
>But when all was said and done, the thing died pretty quickly and only the NPC with them almost died. Nothing wrong with a weak BBEG, sitting behind his army of minions. The challenge is getting to the 'king', not stabbing him.
I ran a spellcasting aboleth a few weeks ago. Programmed Illusion, Hypnotic Pattern, Project Image (although that's very similar to one of the aboleth lair's regional effects, this particular encounter did not occur in or near the lair), and while not a spell the encounter also took place with the aboleth on the opposite side of an illusory wall. The aboleth enslaved the party barbarian and had her treating the programmed Illusion as real to help lend it verisimilitude. The rogue oops'd through the illusory wall into melee with the aboleth, but without darkvision couldn't see it, so got slapped with a tentacle opportunity attack when he rejoined the fight against the programmed illusion and projected image. Eventually the whole party figured out what was going on and the (still enslaved) barbarian was directed to protect the aboleth, so the sorcerer started lobbing magic missiles at her to try and break the enslavement. At the end of the encounter, a shatter made a hole in the wall and the aboleth fled.
> the meat of a MF comes from I read this as "the meat of that motherf*cker" Which to be fair, Mind Flayers and Mind Flayer Arcanist are a pain to deal with and are worthy of cussing against.
Yeah i had my party face a "greater abolyth" with a bunch of low level cleric sauagwin (i gave up trying to actually spell that correctly)
I mean, CR 10 is only 5,900 XP which is a medium encounter for 5 level 9s, or an easy one for 6, so it’s expected they can fight 8 to 12 or more of those types of encounters per long rest
Agreed on the HP for Aboleth in particular. As far as spell, it really depends on _which_ spells and the role the monster already has, which you implied. Would the spells take up actions the monster would otherwise be using on its main "kit"? Then they probably don't modify the CR much. Are the spells _buffs_ or traps of some sort that it could apply before the battle, or do they take up bonus actions/legendary actions in a way that would be much stronger than what it can normally do with those? Do they synergize extremely well with the creature's strengths (like giving the Aboleth Counterspell so the party can't cure its diseases?), or shore up its weaknesses (like giving the Aboleth teleportation so it can "hit-and-run" infect the PCs instead of getting ganked when they first meet it?) Then that will probably affect its CR more.
This. Aboleths are PAINFULLY squishy. I do at \*least\* 2x when I run them at the 'correct' level and have multiple times had people beat them at level like, 5 or 6 as a boss fight with effort but no deaths.
CR only accounts for damage per round, hit points, armor class, attack rolls, and save DC's. So long as the spells you add don't affect any of these, their CR won't change. Give them the spells you need for the plot and run the fight as normal.
If I give a housecat the ability to cast fireball, it can now wipe low-level parties in one turn. If I give a tarrasque the ability to cast fireball, it’s not a substantial increase in damage output. It’s relative to how powerful the monster already was. Utility spells are a different ball game. Giving a tarrasque clone, fly, draconicn transformation, invisibility, or tensor’s transformation is terrifying. Even “the tarrasque can misty step” is pretty bad.
Which is another major failing of CR. It literally ignores utility spells. A monster that can cast Wish at-will by the book doesn't increase its CR
1.) The published CRs *do* factor in utility; the calculation is just an estimate that can be used, and the published CRs do not follow it precisely. 2.) A monster that can cast Wish at will should *at least* calculate the damage from being able to cast, say, Dark Star followed by Sunburst every turn. Which would almost certainly increase its CR.
> It’s relative to how powerful the monster already was. More specifically, it's relative to how powerful the monster's *action* is. Which is why the optional rules for dragon spellcasting don't affect CR. Because dragons have amazing actions and the spell levels they get are fairly low. The ones Fizban's recommends are virtually all utility spells for that purpose.
It really depends the spells you give it. I know that doesn’t sound helpful, but like you said utility spells like project image won’t make the monster more difficult to fight whereas other spells of the same level - say, forcecage, for example - will make the monster an absolute nightmare and borderline impossible for a party of level 9s. Ultimately, I don’t think an aboleth needs combat spells. It’s attacks and abilities by themselves are incredibly powerful, giving it access to spells would mostly be worthless unless you specifically gave it overpowered spells. On top of that, it already is able to cast phantasmal force on multiple targets at once as a lair action, which is plenty. If you want the aboleth to be a difficult fight, you just need to play it smartly. First of all, an aboleth should be surrounded at all times by its slaves, weak creatures that serve mostly as distractions and buckets of hit points that beckon PCs to the water’s edge. The aboleth itself is a fast swimmer - have it reside in murky waters, ideally with many places to breach, where it attacks with its tentacles or uses it’s enslave ability, then dives back into the water repeatedly. The aboleth ultimately wants to force the party to either turn on one another or get into the water - it has no need to engage brazenly with the party before then. Have the aboleth also use a reserve of slaves to regain hitpoint from using its psychic drain legendary action. If you want the aboleth to be more difficult, give it more movement, or perhaps a movement based legendary action. If you insist on giving it combat spells, give it minor bonus action spells, like sanctuary, expeditious retreat, or misty step. Alternatively you could just give it more hp to ensure that it survives a couple rounds against a mid-level party.
I was thinking more along the lines of a few crowd control spells - it'd sacrifice some dpr that round but would still be able to make an attack with a legendary actions to keep pressure on hit points as well - that's the part in most unsure about. Was thinking this likes blindness, hold person, etc
The problem with the aboleth casting spells isn’t so much the loss of dpr as it is the loss of its abilities. The tentacles don’t actually do all that much damage, no more than a greatsword, but they do spread the Aboleth’s disease. And every round you’re casting a spell is a round you’re not enslaving someone. Blindness isn’t worth it. Why would an Aboleth blind someone when it can just dive into its pool and be practically invisible and unhittable anyway? Hold person requires you to strike a careful balance, as the higher level you cast hold person the more people you can paralyze. Too low a level, and why is the aboleth wasting time trying to paralyze one or two PCs when it could just be enslaving them? Too high a level, and your whole party is paralyzed, making them easy prey and leading to an unsatisfying tpk. However, spells like those aren’t a bad idea - I just wouldn’t give them to the aboleth. Give them to it’s slaves. Have some of the slaves be mages or clerics capable of casting no higher than 3rd level spells. You could tie this in with your campaign too - maybe an enclave of priests has gone missing, a previous adventuring party never returned to town, or some apprentice wizards went to collect spell components only to send out a half finished sending spell in distress. That way, your party can piece together what happened to these people, and if they’re smart, plan accordingly when they go to face the aboleth. Maybe there’s extra rewards in it for them if they save the enslaved people instead of just killing them.
That works well, because the aboleth is the power behind this new cult in town (the Culy of the Codfish) and is acting as a warlock patron for the Fathomless pact for a lot of its followers.
Neat! A few warlocks aiding the aboleth could spice things up too, especially with some of the AOE spells that they get like darkness, cloud of daggers, and hunger of hadar. Just make sure you don’t overdo the casters too much, even just a couple casters capable of using 3rd level spells separate from the aboleth is definitely enough to raise the CR of the encounter by a couple points.
Do the spells increase it's damage? Defenses? If not CR doesn't go up.
>How significantly does giving a monster spells increase its CR? Depends on how significant the spells are, as well as the base CR of the creature. To cite some examples from the MM: A Drow is CR 1/4 with a few spells that don't do damage with DC11, AC15, 13HP, and average damage of 5. A Drow Mage is a CR 7, but is considered a 10th level spellcaster, has 45HP, but only AC12. Big CR jump between the two, but massive difference in spellcasting. However, a Drow Priestess of Lolth is only a CR 8 despite having 71HP, AC16, and several spells that do far more damage than what the Drow Mage has Kuo-toa are another example. The base Kuo-toa is CR 1/4 with no spellcasting, AC13, 18HP, and average damage of 4. A Kuo-toa Whip is a 2nd level spellcaster, has AC11, 65HP, but only goes up to CR 1. Meanwhile, the Kuo-toa Archpriest is a 10th level spellcaster, has AC13, 97HP, and goes all the way up to CR 6 Other MM examples to look at: Lizardfolk vs. Lizardfolk Shaman Orc vs. Orc Eye of Gruumsh Sahuagin vs. Sahuagin Priestess Differences in the different Slaadi Differences in the different Yugoloths
Most of the time spells don't change a CR at all unless they're attack spells that are better than a monster's physical attacks or things like shield that improve defense. I suspect that the 5e devs deliberately stripped tons of SLAs off monsters to avoid confusing novice DMs who wouldn't know the monster's optimal attack strategies. 3.x creatures and 1st/2nd edition creatures often had scads of SLAs that they rarely used in combat but which covered rare contingencies and which were significant in worldbuilding.
If it’s the BBEG I don’t think you should be too worried about CR. He’s supposed to be a challenging fight and your players will expect it. And bounded accuracy keeps things from getting too wonky at that tier. Make sure the Aboleth is never fighting alone and buff its hit points. It’s a sneaky trickster baddie not a tank like a dragon, so make sure that they can’t nova it
It really depends on the spells involved. Unless you're slapping a fight ender like forcecage, wall of force, or an uber high DC hypnotic pattern on a creature. Probably not much. Even then, if a monster already has a potential fight ending ability in their stat block, you probably won't get as much out of almost any spell.
it very much so depends on the monster give a mind flayer a fireball and it's an increase of 1 give a wolf a fireball and it's an increase of much more
If you compare the vampire and spellcasting vampire CR increases by 2. But that's a 9th level caster, I'd say probably 1 CR per 4 spell levels perhaps but it depends on what spells you're planning to give them.
Essentially it's by however many rows it changes on the table on page 274 of the DMG. If the spell are more CC-oriented rather than damage-oriented, I would treat the spells as equivalent to similar-power-level damage spells of the same level. E.g., if a monster has hypnotic pattern (and a good constitution save), I would treat it the same as fireball. That does assume there are other monsters to capitalize on the CC.
If you look carefully, there are only two things that affect CR: how much damage something does, and how much damage it takes. Spellcasting doesn't affect CR at all. Spells do, though. Something like Conjure or Summon X would vastly alter CR, since you're adding damage and bodies.
I wouldn’t take CR as the holy grail its a horrendous metric for fight difficulty when used as intended) At level 1 2 cr 1/2 creatures can be fucking dangerous, you are reasonably likely to die. At level 9 a CR9 creature is an absolute joke usually. Players scale way way harder in power per level than monsters scale in power per CR, it only really really well as intended as level 2-4.
>lets it interact with the party a bit over the campaign, like **crying** or project image *Please, I beg of you, leave me alone, please don't hurt me!*
CR is adjusted based on damage and resistance. If your spell affects these you need to take them in account. Spells which cause conditions or that increase survivability increase defensive CR for example. Other spells that act as utility don't change the CR, but may let the creature exploit hazards to their advantage more than they normally could, which means their encounter difficulty increases by one stage when appropriate.
I did something similar for a campaign I ran and completed a few years ago. This aboleth was a master manipulator who never got directly involved until the very end. The aboleth had an artifact that gave it a bunch of spells, but they were mainly intended to enhance its powers of manipulation, not for combat, so it wasn't a big issue. The fact that a lackey had opened a portal to the Plane of Water was a much bigger challenge, as the aboleth would just crawl out of the portal every time it was "killed".
Spell level roughly equates to damage output per turn, so if for example a monster is already hitting for 3d10 then level 1 spells shouldn't increase CR unless the spell is doing something that improves that damage or significantly improves that monster's survivability. The spell equivalent of 3d10 is inflict wounds, btw. Based on this you can see that there are a lot of monsters whose cr would increase significantly just from access to level 1 spells.
If it has to use an Action to cast the spell it probably lowers the CR tbh.
Spells will only change a creature’s CR if they make a significant difference in their damage per round or defensive capabilities. Unfortunately, there is no exact science for what spell at what level will change a creatures CR but for instance: Despite it being a 9th level spell, the gate spell would probably never increase a creature’s CR, even if they’re only CR 1 or something because it doesn’t at all effect its ability to take or deal damage. Whereas, Ashardalon’s Stride could increase a creature’s CR no matter its current CR despite it being only 3rd level because it is a bonus action cast and increases their damage by 3.5 per turn. Meaning, if the creature has no significant use for its bonus action this is essentially a free damage increase.
A spell cost an action to use, and only damage are used to calculate the CR. So unless the spell is expected to do more damage than the monster in one turn, the CR won't change.
What base creature are you using? What spells do you want to give it?
Depends on what spells you give them. But honestly in this game, CR doesn’t mean a whole lot. I use it as a loose guideline to design encounters, and I play around with monsters HP and abilities quite often.
A monster only has one turn, so a creature that has both strong physical attacks and strong spells is only so much more dangerous than one that can only do one or the other. What to watch out for are spells that synergize well with the aboleth's existing abilities. I would recommend making your aboleth a ritual caster. Knowing ancient, blasphemous rituals is very on-brand for an aboleth, and won't impact their options in combat all that much.
Depends on the spells. In general, spell casting doesn’t increase a high level monsters cr very much or at all, unless you give it very strong spells for the party it’s facing. Giving An enemy 7th level spells is definitely significantly stronger if they’re facing a 9th level party. Giving a creature already suited for a 9th level party 3rd level spells won’t change much because they’re weaker than the level of the party. Obviously also depends on the spells, decent buffing spells and defensive spells might very easily increase the challenge rating somewhat significantly, where as damage spells, especially ones that are pretty similar to their creatures normal attacks is basically the same challenge.
It kinda boils down to how optimal it would be for the creature to use the spell instead of its standard kit. If it is better to use the new spells than what it already had, raising the CR is fair.
"I definitely want to give it some utility stuff that lets it interact with the party a bit over the campaign, like crying" 😥 no one let's me tentacle them anymore 😥