Bogarus Quick Guide

[Baalz]

Blood vengeance: will reduce the amount of hits they take
Iron skin: 20 protection will stop a decent amount of attacks from dealing any damage (depending, of course, on what they're fighting)
Mistform: those attacks that do land will only deal 1 damage

You'd have to have several of them for this type of tactic to make any sense, so you're talking about a group of them, not a single guy who's quickly surrounded. So...depending on what you're facing it seems likely they're only getting hit for damage a couple times a round, and each hit is just doing 1 damage. With a little bit of regeneration this turns them into something that requires a specific counter.