Hmm, I dunno. Karl's got a scary weapon, but any CC character worth his salt will be ignoring his armour save and will have a decent ward of their own.
I'd still be wary of sending him up against a Chaos Lord, or an Elf. Heck, a Beastlord could be a problem, and Doombulls can be very scary.
Blenderlord's possibly the only build that is very likely to kill him though, on account of attacking first and getting additional attacks in. Every other character might not finish him off before he gets a chance to swing - though he could easily miss or bounce off a ward.
I think he should be OK, but best to be wary of the powerhouses just in case.
EDIT: Malekith could ruin him, but he's a bit hit and miss...