With tons of chaos drives and animals.
Attack it. Also, it's Sonic Adventure 2 Battle.
you need to give it alot of green chaos drives(the little cristals that you get when you kill robots)
Sonic Chao turns blue on it's second evolution.
Play a level, get the chao key by breaking open a chao box and finish the level.
finish a level with a chao key Found in a chao box with shadow
In Sonic Adventure 2 battle a chao that looks like sonic would be neutral/running/running you could give it chao fruit just as long as the skill with the highest level is running for both evolutionary cycles.
beat level 3 in races
this is how i did it i traded my chao from sonic dx to another chao from sonic advance 2 for the GBA then i traded that same chao to my one of my chao in sonic 2 battle
Giving it tons of chaos drives and animals.Simple as that.
No the chao gets sonic hair.
Easy eat a chao with all characters and go to any sonic level.
You have to trade the chao with some one else