Twilight: "Let me guess (Sips coffee) we're going up another Evil Sealed In A Can that 'Tia forgot about until now? (Sigh) Seriously, Princess? Can't ya just kill one of these guys just once? Sure it's not proper for the show, but at least they wouldn't be coming back after 1000 years....unless they knew Necromancy...."
Celestia: "Twilight, we tried killing one once. It... didn't turn out too well. He just found replacement parts for whatever we destroyed." (Discord appears, looking irritated) Discord: "Speaking of which, Tia, you still owe me two arms, two legs, four hooves, a tail, a torso..."