That's awesome looks like they would fit into the game quite well, but no art would be completely good without some criticism.
Not on the art itself, but the explanation. What exactly is it a mutant of? Obviously humanoid, but it has the ability to swallow them like a snake.
Yeah, it's supposed to be a human. Probably not swallow like a snake, but with such a big mouth, they just gulp things down. Being like a snake is something I just pictured as I posted it, and it would need a revision to be more like that, and would probably be like a centaur, but more snake like. I don't know whether or not to have them originate from Vault 87 or from Mariposa Military Base, but FEV has been shown to do some crazy stuff, and I wouldn't be surprised if there were other locations with it. They're smaller than super mutants, have a wide mouth that goes across half of their big head, and multiple eyes letting them have a FOV of about 270-300.
I could make it look more spider like, going off the eyes. A mutation between human and spider? A messed up spider-man.