While Crossbones was incarcerated at The Raft after having been kicked off the Thunderbolts, he was attacked by Mo Money and his crew. Man-Mountain Mario ended up helping Crossbones in the fight because he looked up to Crossbones for having been a Thunderbolt, a villain turned hero, a second chance that Mario aspired to. When The Raft came under attack during Fear Itself, Crossbones, Mario, and Mo Money and his crew used the opportunity to work together and escape.  
Hours after their escape however, Warden Walker and Mach-V were searching the area for escapees and came across the bodies of Mo Money and his crew, as well as Mario with Crossbones' ID tags, all having been killed by Crossbones after making it out of the wreckage of The Raft. As Mach-V surmised, Crossbones had merely kept Mo Money and his crew around long enough to use them to help him escape, and he kept Mario around only to be used to try and fake his death, as he was of similar height and build to him.