He could hit at the 40's but these hits are infrequent, and a frequent hit is about 10 or 15. You can use lobsters but swordfish are best here. Make sure to bring Prayer Potions, as well. Once you have him at 10 hitpoints use the book that Willus gave you to cast a spell which can finish him off. After he is defeated he will fall Magical Bones. Take these to Willus to demonstrate that you conquered the beast. Now speak to King Vargas and decide to tell him what happened. Luckily Willus has already told him everything. Congratulations, quest complete.
I really want something like a free for all stadium as a safe minigame. It could be quite fun and fantastic XP. The area would be about the size of the fist of guthix stadium with a great deal of challenges, ranging towers. . .etc. It won't supply runes, but it is going to return about 60% of the runes you've used.