[[Image:Mon-mephisto1.jpg|frame|left]]Mephisto is the act boss of [[Act Three]], and must be defeated to complete [[Quests_Act_Three#Quest_Six:_The_Guardian|The Guardian quest]] and to move on to [[Act Four]]. He is brother to [[Diablo]] and [[Baal]], is the first of the three [[Prime Evils]] a player encounters in ''Diablo II'', and appears in the game as a skeletal, floating, legless apparition. Mephisto battles at melee range, but also possesses a wide variety of powerful enchantments, mixing lightning with poison and cold damage.