The Deviants (also known as The Deviant Ones) are a gang of delinquent children who carry out various tasks for Mister Melmoth. They seem to be comprised primarily of various street urchins and runaways, with older members teaching newer ones various tricks of the trade. It's up to the children who leads their group, but it usually ends up being the eldest. Once the eldest turns 16 and has to join Team Red, a successor to lead the Deviants is usually chosen by the previous leader.
Billy Beezer was the current leader of the Deviants when Melmoth recruited Klarion onto the team. With Klarion's help, the gang easily snuck into the Manhattan Museum of Superhumanity to steal a WWII drill vehicle for Melmoth. Upon returning to their employer, Beezer began proclaiming his dislike for Klarion, doubting the fact that he could make a good leader for the gang after he himself turned 16 later that night. Klarion had no interest in leading the group, as he was just exploring the surface world, but he wound up fighting Beezer after he attacked Klarion's familiar, Teekl. Beezer was about to pound Klarion, until the witchboy threatened to tell Beezer the hour and date of his death. Unnerved, Beezer backed off and the gang went to bed.
Later that night, as the clock began striking midnight, Beezer was awoken from his bed by Goldenboy, the previous leader of the Deviants. Beezer shared his unease about joining Team Red with Goldenboy, who reciprocated by telling Beezer of how Team Red was nothing more than a relentless hard labor gang who had to gather gold for Melmoth. Mister Melmoth then arrived and told Beezer of how he was 16 now, a man, and a man needed a job. With that, Goldenboy grabbed Beezer and dragged him through the gateway that would take him to Team Red.
As it turned out, Klarion had been using Teekl to spy on Melmoth in order to confirm his suspicions of the man. The rest of the Deviants learned from him of what lay in store for them, and so they desperately looked to Klarion to lead them away from Melmoth. Klarion declined however, and instead told the children before he left that it was their own choice whether or not they decided to stay with Melmoth and eventually become his slaves.
It's uncertain what became of the remaining Deviants, but it can be assumed that they left Mister Melmoth's employment after he was defeated by Frankenstein.