How do you make a dark chao?

Just use Shadow, Eggman and/or Rouge to raise a Neutral Chao into a Dark Chao and then maybe a Devil Chao like you used Sonic, Tails and/or Knucles to raise your Neutral Chao into your Hero Chao and then Angel Chao! Good Luck =)

All you have to do is keep petting your chao with the dark characters.

Use shadow then feed it dark fruits and pet it with shadow.

Use shadow rouge,eggman,or shadow only.

I heard you have to be mean to it as good characters and nice to It as bad ones aka good is sonic tails and knuckles and bad is shadow dr.eggman or rouge

Pet the chao with Shadow, Rouge or Eggman until the Chao is completely black. Then you feed it fruit that grows on the trees in the garden until it's stamina reaches level 6. Then your chao will enter a coccoon. After waiting for a bit y
Ou have your own Hero Chao!

Pet the chao with Dark Characters (Shadow, Rouge and Dr Eggman) or abuse it with Hero Characters. Petting the Chao is better than abusing it. If you are in Sonic Adventure DX (Or too lazy to get Dark Characters and you want to avoid abuse), Feed it dark fruits (Or get Dark Seeds with a chao who has a shovel and the elephant watering can). The dark fruits costs 120 rings and the dark seeds costs 400 rings (Seeds only available for Sonic Adventure 2 Battle)

Go 750 mph on the little guy's head with sonic. He'll turn to hell.