On our last trip into OI we decided to kill every mob in the place just so we could say we had done it. Our raid was a trio - Matt13f_HM (Priest #1) Dustoff (Priest #2) _JAX_ (Fighter)
Before heading to the two fat bosses and the blue haired boss we decided we would run around the map to check for any we may had missed. We found Evilmidget Clavi in an area we had been in before so he must respawn in this area at some point. We are not sure what it takes to get him to respawn but some of the best theories are
1) You need to kill off all the bosses first (except the 2 Fat bosses and blue hair) Tried Failed
2) You need to kill a majority of the mobs Tried Failed
3) Its just a waiting game. Like almost all bosses in the game they have a respawn time Tried 4 hrs Failed
4) Its just a chance encounter and we got lucky Seems likely
I will say this. Its worth it to find him because the drops OMG! I'll leave it at that lol.