Some TMNT stuff really isn't for little kids.
In the IDW continuity, Colonel Fist is the leader of a gang of four of mercenaries hired by Madame Null to capture Dreadmon. Like his cohorts, he is a human-born mutant with cyborg enhancements that allow him to shift between human and mutant forms.
His team successfully tracked down Dreadmon, but their mission was complicated by the presence of Sally Pride and Man Ray. After Sally and Dreadmon escaped, Fist ordered Deadaim to stop their car by shooting out the tire, only for Sally to soon return fire, which he deflected with his cyborg arm.
The conflict paused when Fist informed Dreadmon that they were there to recruit him rather than kill him, and that their ability to shift between mutant and human forms was one that could also be given to him. However, Fist also demanded that he show his trustworthiness by killing Sally, which Dreadmon refused to do. Fist's order for Waster to kill her was interrupted by Ray hijacking the team's vehicle, forcing the mercenaries to pursue them on foot.
Fist tore the roof off the vehicle and attacked Ray, only to be shot into the road by Sally. He was injured, with skin scraped off his cyborg skull, but was otherwise unhurt. He ominously implied that he and Sally would meet again.