I think it would be fun if people could join arena tables against boss type monsters. Ideally the battles would be insanely difficult, with those trying to play against the generated bosses/monsters being at a huge disadvantage (the sort where they would be expected to lose 4 out of 5 times). Not only would it be structured to be difficult but players would recieve points for winning that would kind of add to the strength of their characters, kind of like power adds to the strength of pets. The more you play the more points you rack up and the more the creatures become buffed in adjustment to your points going in. This means eventually it should become so hard for you to win that you are unable to advance, but because it makes you stronger if you should ever again succeed you are prone to keep trying and trying, which of course would be an extra incentive for players to buy better equipment in hopes that they can advance just a little bit more.
Okay, perhaps this isn't the best idea, but I always wanted to be put up against bosses that all use scarecrow and so forth, and if it is made like a guantlet that gets harder and harder, well, to me that is fun.
