A feared and overconfident demon overlord, he eats hot coals for breakfast!
Moloch's modest health (11111) is helped by the dangerously fast time that he could walk to the exit. Other than Vez'nan, he is the only boss to possess an area instant kill attack (other bosses only have either area attack or instant kill); and he can use it on every unit (while Earth Elementals are immune to Vez'nan's). His path is very short, combined with his above average speed and ability to quickly clear units designed to stall him, he can easily overtake an unprepared player.
He will only use his area instant kill when there are multiple enemies. Use this to your advantage and block him with Heroes and Earth Elementals. This attack is also tied to a cooldown, he will use it after about 2-3 regular attacks