Also I think you should introduce a new set of antagonists who are just straight up evil loose canons who are loyal to no one but themselves that Xixi might go to when she's desperate for more firepower. I'm thinking a couple of mad scientist black market doctors who are also a brother and sister to reflect a dark version of Gina and Greg. They use themselves as test subjects to inject illegal muscle growth drugs with monstrous side effects that mutate their bodies to look distorted, twisted, and purple and it warps their faces into looking demonic. These two could be the ones responsible for the creation of Xixi's executioner (who could then turn out to be just one of many manufactured executioner clones they created).
Even if you don't go with it fully, consider making some kind of a muscle duo of mad scientists who are just a dark "Chaotic Evil" reflection of Gina and Greg but ones that the Mafia turns to when they are desperate and you could build your own character profiles around that concept.