Haha I loved the killer dolphins one. They outta just make Treehouse of Horror episodes instead of the regular ones. They're always the funniest and the most clever.
Oh and they're just koalas! They are in no way bears. Didn't they ever teach you that in school?
Try taking a joey from one and you might have a killer koala. Imagine
Joey on a koala's back. Scary thought lol.