Knights of Tezoth

Dorian could kill anyone in one hit with a guaranteed strike and also had invisibility. And no, he is not an assassin)

Believe me, such a character can be countered too. Dorian doesn't have any AoE spells, does he? In that case, it's enough to overwhelm him with meat. Or with an opponent who ignores the first attack. Anti-invisibility abilities also exist in the expansions. Somehow, on Heroist, an assassin with permanent invisibility died to a simple pirate. Something I still feel guilty about, since they were saving my character there.