(this is in fact just about the only fight I ever do in TBM) because he recovers roughly 200 HP per turn and if you are fighting in real-time he has a whole bunch more chances to recover. In TBM he only has one chance to recover for every 4 times you hit him, so as long as you do more than 200 HP per round you'll kill him easily.(Also note that the two black chests behind him respawn every time you enter the cave, so once he's dead set a beacon next to one of them and you can teleport back in for more cash or items whenever you want (until such time as you have all the artifacts/relics the game will allow, then you just get cash).)
... (spoiler)