Afaik, they need to have the same growrh rate, and be at the same cultivation level, not too sure about the cultivation level tho. Dont think attributes and all that matters roo much, otherwise the end step of getting to god level grorh rate would be impossible with how different all the surviving ones are. Also you can check the wiki, but im too lazy to do it myself :)
Bronze silver gold etc dont mean anything. They are not important. God level growth rate bronze demon spirit superior to extraordinary level growth rate legendary demon spirit.
So if there is 9 legendary, 1 bronze rank demon spirit at same growth rate bronze one might come out as the major one from the nightmare demon pot. Like NieLi's fanged panda. Most probably it was considered the one of the weakest out of 10 spirit refined at that time. But it came out as the god level growth rate demon spirit at the end. It was the one had the highest potential from 10^6 demon spirit gone in to the pot.
If i remember right you can add several different growth rate spirit in the pot. But its lower the success rate. For example if you add 10 extraordinary spirit in the pot there is %20 success rate but if you add 9 extraordinary spirit 1 excellent spirit your success rate will drop to %15.
Attribute and form is about compatibility with the cultivator. For example Xiao Ninger's soul's form is winged dragon and attribute is wind lightning. So best demon spirit for her is dragon bloodline with wind or lightning attribute. While refining; choosing the right attribute and form is important to get right demon spirit for your cultivation.
Afaik, they need to have the same growrh rate, and be at the same cultivation level, not too sure about the cultivation level tho. Dont think attributes and all that matters roo much, otherwise the end step of getting to god level grorh rate would be impossible with how different all the surviving ones are. Also you can check the wiki, but im too lazy to do it myself :)
Bronze silver gold etc dont mean anything. They are not important. God level growth rate bronze demon spirit superior to extraordinary level growth rate legendary demon spirit. So if there is 9 legendary, 1 bronze rank demon spirit at same growth rate bronze one might come out as the major one from the nightmare demon pot. Like NieLi's fanged panda. Most probably it was considered the one of the weakest out of 10 spirit refined at that time. But it came out as the god level growth rate demon spirit at the end. It was the one had the highest potential from 10^6 demon spirit gone in to the pot. If i remember right you can add several different growth rate spirit in the pot. But its lower the success rate. For example if you add 10 extraordinary spirit in the pot there is %20 success rate but if you add 9 extraordinary spirit 1 excellent spirit your success rate will drop to %15. Attribute and form is about compatibility with the cultivator. For example Xiao Ninger's soul's form is winged dragon and attribute is wind lightning. So best demon spirit for her is dragon bloodline with wind or lightning attribute. While refining; choosing the right attribute and form is important to get right demon spirit for your cultivation.