Heya!

Looks like a pretty interesting class/job. The only thing I would argue on is: Wouldn't the Joker mess up with the aggro? Because he'll have, say, 10% of aggro while the tank has it 90%. Once he provokes the target he'd go 100% and the tank has to re-provoke it to maintain emnity stable.
Seems like a ball on the foot for tanks and the whole party itself, because if the Joker is gonna get KO'd, then the monster will aim to another party member, and maybe not the tank.

If you ask me, I'd prefer something that doesn't provoke targets in order to direct them at it, but something that would give buffs to the party members, AoE heal the sh*t out of them and debuffs enemy targets. Something like a Dancer or a Musician.
Aw man, I'd like to see an Attack Boost with a Heavy Metal background or heavy drums, also a Serenade to augment the HP regeneration.
I fail on do threads, because I don't like to write long (lies), but if you approve the idea and would like to do one, you're free to do it. Disciples of Rhythm =D