Jondar Infinite Skeleton Glitch
First discovered in the open beta of Diablo III, the so-called Jondar glitch occurs if and when you town portal out during your fight with Jondar in the Tristram Cathedral. You encounter him after you help the Templar recover his equipment from the cultists.
Clearly, when the developers were testing the game they didn't think anyone would think to cast town portal while he's summoning skeletons to aid him. If you stay in town long enough and re-enter the portal, you'll return to a literal horde of skeletons that Jondar's summoned.