Plesioth from Monster Hunter. If you've ever fought one, you'd know why. Here's a brief run down on why it's the most annoying shit ever, and should be removed/fixed (I don't know why Capcom hasn't yet).
First, it's a water monster, and you can't go in water, so you need to wait for it to pop out onto land, which can take an ungodly amount of time. Otherwise, you can use a sonic bomb, which puts it into rage mode, meaning it attacks faster and does more damage. It also deals TONS of damage to begin with, so avoiding rage mode is a good idea. It's hitboxes are just completely fucked, meaning the tail can be waaay over your head, nowhere close to touching you, and do massive damage anyway. It's notorious for its "hip-check," where it slams its body at you, which is the most bullshit attack ever. The hitbox for it basically the entire room you fight it in, and it can pull the attack off before you get the chance to roll out of the way. Also, it has tons of health.
gunbladejoe said:
is that picture from fallout 3? if so what weapon is that?
I'm going to guess it's the unique Gatling Gun "Vengeance."