Master of Bludging
Their biggest problem though, would be to find someone with enough power in their name to replace him. The Tryant Kuma is a name pirates know and fear. I mean even someone like Luffy, with all his feats of invading and pretty much destory all 3 of the world goverments main islands, damn rooks like Caribou reckon they could take him on. While Luffy has a name, it isn't much to scare off the stronger pirates of the day. Even Law had to go out of his way to make himself stand out (appearing at the war and saving Luffy, 100 hearts etc). Buggy is a simpiler one as he has history (even if his unworthy), was at the war, and has been shown to be a comander of a group of convicts of some significant strength. Much like the Yonkou, his crew is filled with bounty headed pirates, who's numbers alone would scare off opponents. Who knows, maybe even Caribou was after joining his crew.