They spawn practically on top of the entrance portal, unlike the wild ones in Mechagon, where you had to complete most of the dungeon! Of the 20 odd resets, they usually spawned in sets of 2. If there isn't a catchable pet and they spawn in as a critter, head out and reset. But you don't have to do any of the dungeon to catch them, no stressing over ilvl, waiting until a new patch or simply getting invited to a group. I have no information on Rarity, though, and obviously, one of the bosses can drop a pet, so you still may wanna run it eventually! Hope this helps someone!
