Why is your chao not evoling into a devile chao

your chosen chao must be a normal egg, for example when you start a new game or unlock a new garden it has normal egg(s) in it

your chosen chao must be reincarnated twice, then given 1 of every single animal.

You have to do all of this with a dark character.

-Rouge
-Shadow
-Eggman

When it evolves it will be a devil chaos chao! Have fun!