I did it on my level 46 melee pure. Don't fight anything you don't have to fight. Take lots of super energy potions, prayer potions (if you have prot prays, I did it with no pray) and other stat boosting potions. The maze sounds hard, but it's easy if you bring the energy potions & food.
When it comes up to the demon, take your BEST POSSIBLE KO ATTACK with you and stay in the safespot (which is crossing the bridge and moving left/right). Lure the demon into the gnomes while you're in the safespot and when it's on low health (too low will make it regenerate) use your KO attack.