Mistwalkers are enemies that utilize a very deadly poison that rapidly deals heavy DOT.

Countering them varies per class.

Warriors should either be tanky enough to endure the poison once or twice or utilize their stuns (Brutal Advantage & Heavy Shuriken/Blackout Stun).

Generally, you shouldn't give them the chance to poison you (stay at range/use stuns/burst them down), unless you're durable enough to tank the poison.