Piranhas are definitely a big threat in packs, but if it’s just one then I think Sharktopus should have this round. He’s a pretty powerful monster and he’s always ready to rumble! He’s definitely been on a roll lately and things could be looking pretty good for him on the blog. Sharktopus wins.
DReager1.com 
You really have no idea how tiny piranhas are.
I probably do overestimate those guys, but they look so strong in horror films!
Horror films aren’t the best source for factual information. Besides that, the Red-bellied piranha(which I assume is the piranha you’re using; there’re several) is only 33 cm and 3.5 kg. Tiny but nasty.
Heh heh, well that was mostly in jest. Still, the Piranhas are definitely very small. Their bite is serious, but as long as you have a big stick, you’ll typically be fine. If you’re fighting underwater, then it gets dicey!