When I beat the SOB, I used Chaotic maul with Bandos, and an Extreme set. I had a lot of problems trying to beat him with magic. W/ Melee, just keep interrupting him as soon as the skill timer resets. Every time you activate it, it stuns him, even if he's already stunned. An inventory with about 3 prayer flasks, An Extreme set and rest rocktails did me.