When I did it, I brought 20 sharks, 3 prayer pots. Turns out: I only needed two sharks. I was 47 Ranging, I brought a Yew Shortbow. I expected it to be super-hard, but it was really easy. I was in the Castle Wars arena... and I clicked my sigil. Too bad I forgot to click Protect From Magic. So I got there, and the demon started to hit me with magic. GAH! It hit me a 27, then a 22. So I worked the magic of my one-click teleport - the Ectophial! I ate my shark, put on my sigil, put Protect From Magic, and I didn't get hit a bit during the fight. It took me a minute. The trick is: stay far away from the demon so you can't see his HP. Range at him (I brought mithril arrows), and he will only hit you with magic, which you're immune to. Believe me, the gnomes did at least 3/4 of the damage. =D So that's my story. Good luck!