you read the title, im homedrewing up a domain of dread where whenever a creature takes a long rest, they roll on a cuple of tables to see if they evolve or devolve and what happens. any ideas for things I could put on these tables?

also, don't worry, remove Curse will put you back to normal

You could have some simple things like increases/decreases in ability scores, speed, armor class, or other things. 

This is a bit more of a mutation but you could have them gain some abilities of monsters along with physical features. Some examples could be-

• Displacer Beast - Makes you appear more illusiony , there is already a magic item that does this so you can just give them the benefits of it.
• Any flying creature - They can sprout wings and gain flying speed
• Ghost - They can travel through solid objects to an extent(maybe with a 10 foot speed and they revert back to being solid at the end of their turn.)
• Dragon - They gain a breath weapon similar to the dragonborns but maybe more powerful.
• Doppelganger - They are able to cast disguise self at will.
• Vampire - They can get some of the positive vampire abilities like the mist or regeneration or they can also get the vampire weakness feature.

Hope these ideas help.