>>9238767For Marvin, you can use pic related with a WWE Mutants Stardust's head and hands. You'd have the general proportions down, and with minor modifications, you could easily mod in some much needed articulation points into the Alpha 5 body.
In Carl's case, I'd say you have a few options. Namely, ML Frogman, one of the many tentacle-less toybiz Doc Ocks (the movie one, series 8 one, or web splasher doc ock) or better yet 9ne of the huskier WWE bucks. This guy made one out of an elite Umaga.
https://figurerealm.com/customfigure?action=view&id=110364 