Champion: Raise Rookie's level to 5 and it will have a Digivolution.
Ultimate: Raise Rookie's level to 20 and it will have a Digivoulition.
Note: Ultimate Digimon learn their Signature attacks from the show at level 70

In battles when the static bar goes all the way up, you will digivolve to your Ultimate form. You are also healed completely.

Digimons digivovle to Mega forms at level 40.