some such as kamado, if your kamado make it so if your a demon you are immune to the sun. This will make it more realistic ngl and bring more people.
Another one is himejima, if you never add stone breathing to the game make it so you only have one move of stone breathing and you get a health boost.
Last one is kocho, it would be really cool and bring more players if you make it so when you kill a kocho family in pvp, you will get a poison which can take half your hp away. But if your a kocho without insect breathing then it wont work, this will make it so its not overpowered and any kocho can use it. If you are not kocho and have insect it will not work.