Corpses are left where they died. If it's turned into a zombie, it's spawned on the nearest ground it can stand on. Its equipment will be left where it died, however.
By wizard room I assume you mean the room that spawns beyond Elpuri, with lots of spellcasters in it. It's usually a long, narrow room of octiron, with mages, necromancers, mystic frogs and golems. The ones you want to take care of first are the necromancers, there's a lot of them and if you let them they'll teleport all over the place and make zombies of everything they can. The golems should not be a priority until you've killed most of the spellcasters.
Only rats and frogs can swim, and dolphins must be placed in fluid, so far as I know from messing around in WM. My guess would be Oree gained levitation somehow, moved over the blood, then lost levitation, dropping him into the blood and drowning him. Teleportation wouldn't have dropped him over the blood, as teleportation doesn't allow the target to be moved to a place they can't go (walls, fluids, etc).
I thought the only foods that couldn't be wished for were liquids, which is why it's possible to wish for cerumen, 'cus it's not liquid. If holy banana flesh can't be wished for, it wouldn't take much to make cerumen unwishable as well, right?