Laharl will be more than happy to put Mid-Boss down in the arena. As far as the Castlevania folks, Dracula will have his minions in full force even transferring some of the stronger folk from the Inverted Castle to the main courtyard to handle the defense so he can see about binding one of the spirits to his will and getting a foothold over the others. The rest of the denizens will be free to either explore and experiment or help with the defense, with the one order to not approach the barrier.