His real name is Bubba Brown, and was bestowed with the ability to transform into Bubbasaur by Milestone Comic's signiture Big Bang. Later after being further experimented on by SYSTEM, Bubba could also breath fire.        

After witnessing the Big Bang, Bubba left the gang life and went to high school determined to finish and better his life. Though he had turned over a new leaf, he still had a bad temper. The teachers at his school all doubted his change and consistently gave him grief and anguish. Until finally one day he couldn't take it anymore, after being wrongly judged by a teacher Bubba was sent to the principal's office. Principal Carlos Quinones Sr., the father of Blood Syndicate member Fade, expelled Bubba without even hearing his side of the incident, and went so far as to tell Bubba that he should save the taxpayer's money and kill himself. Bubba lost his temper and later on that night transformed into Bubbasaur to exact his vengeance. He first ate the school counselor, Ms. Capri, for not helping to over turn his expulsion. Bubbasaur then stalked the principal all around the school, taunting him about how he would taste. Eventually Bubbasuar came into conflict with Fade, who was in the area to see his father. After saving his father, Fade engaged into battle with Bubbasaur and almost killed him by ripping through his head with debris.

Bubba was saved by SYSTEM to be used as a bang baby soldier, but eventually he escaped the facility along with other kidnapped bang babies. Was last seen as a member of Pyre's new Blood Syndicate. He was also Rocket's initiation opponent into the Syndicate.
 

MILESTONE FOREVER #1

 
Bubbasaurus, as member of Holocaust's Blood Syndicate, was envolved in ambushing Icon. He was easily defeated by Harm, who revealed himself to be an undeercover cop. He didn't have any dialogue, but this may be due to DC tampering with the original format of the comic.