Lord Takeshi casts the most deadly and biggest poison cloud among them. Unlike the poison cloud from other enemies though, his is centered aroud the user, not fired at you. The poison will stun you and deal massive damage. He also throws homing chained kunai that slow you, and he has a powerfull passive healing buff.
Depending on your build, you should either try to sit back and damage him with ranged attacks (priest, some hunter builds) or perform hit-and-run attacks (assassin, hunter, warrior). If you have a melee build you'll need to save one or multiple (depending on cooldown) abilities that can stun him or interrupt his casting of the poison cloud.