That's about what I had in mind. Mostly just take existing bosses and ramp up the difficulty while tuning it to solo content. Would have to prevent kiting for the most part or Brd, Smn, Sch, and Blm are going to laugh at the bosses. Lots and lots of insta death mechanics, some mechanics similar to Urganites in FFXI where you need to do somthing to open the boss to damage or you'll never beat the fight before the timer or your HP runs out.

Maybe have a few bosses special made for the arena, platinum fights you have to pay gold tokens to unlock or something. (Key word: Unlock, not enter. We want people to have to die a bit in this place and losing a big investment like that would turn people off to the game) Make em break the normal play style of the game, a crash bandicoot style chase boss without the bastard camera angles, stuff like that. What they could reward I have no idea, maybe just gold tokens with the real reward being the fight itself and achievements.

I've slept since I thought about this last and it still seems like a good idea so I guess that's a good sign lol. Thanks for y'alls time.