Dec 31st 2009 9:10AM They've got magtheridon in there because they're stealing his blood, and using it to create fel orcs. Remember all those fancy machines in the blood furnace? Yeah, makin' dem orcs.
Sunken temple is reasonable, a green dragon has gone bonkers. He was evidently (WoWwiki) sent to deal with the troll threat in the temple by Ysera, but did a bad job and got captured, and corrupted by the old gods.