Still think a monster puffer (full grown mbu) could beat up just about anything. I mean if you can crunch a fully closed, in the shell clam like an M&M there's not much competition. Also their skin is ridiculously rubbery/tough, they can theoretically inflate, and if something does manage to kill/hurt them it's probably going to die too due to their poison.
Sorry for derail!
Sorry for derail!