Mason Forrest was a student at Hill High.
Mason played for the Hill High Hawks, where he under a demanding coach. To meet the high bar of the coach's expectations, he took slappers. He quickly became addicted, and to finance his new lifestyle, he turned to theft. Together with Dirk and Jody, they burglarized several stores while also using Slappers to enhance themselves to fight away any security that might catch them. One of these heists resulted in an encounter with Batman, whom unbeknownst to them was in fact one of their classmates Terry McGinnis, who likewise recognized him after one of his friends called out Mason's name while Batman restrained him. Backed into a corner, he then used some slappers to easily overpower Batman and have him and his friends escape.
To those close to him, it was obvious Mason took slappers. Coach Creagar looked the other way, but his girlfriend Chelsea wanted nothing to do with it and even the other slapper users started to get rather worried about Mason's conduct. In the mean time, his addiction was growing by stages. First he used slappers for a game, which soon elevated into a secondary stage of using slappers for practices, followed by a tertiary stage of being unable to do the most basic functions of everyday life without slappers. When Batman confiscated their stash, Mason and his friends were forced to sober up. They struggled with withdrawal, doing poorly in practices. When they played without slappers for the next game, they lost, convincing the group they needed to win as well as get a slapper hit to "cure" them of their withdrawal symptoms. Fortunately for them, one of them had stolen a cash card, which Mason takes to the next drop off. However, Batman is watching and interrupts the delivery. The car speeds away but Batman puts a tracer on it. Mason was so pathetically needy that he attempted to chase the speeding car. In doing so he tripped then was apprehended by the Gotham police.
After Batman broke up the slapper ring, Mason's friends were also arrested and Coach Creagar was placed on leave pending his knowledge and condoning of his team's slapper use. However, Mason was seen briefly in future episodes, it was likely that he was sobered of his slapper addiction due to Batman's impeding of production, and whatever punishment was granted to Mason has now been served.