When going in dungeons with the quest defeat Fireblood Beta Spitters, the game will cause enormous lag when nearby one of these elders. When encountering normals of this kind, everything is fine. But when encoutering the elder versions (basically the quest beasts that you need to kill) the game starts lagging. Luckily I was playing with a friend, he could go ahead and kill them. He doesn't seem to be bothered by it so it's a very specific bug. Had it before in dungeons, always with this quest.