I had an (5e) AL gm throw the Tarrasque at a party trying to take a long rest in a dungeon as a random encounter. The paladin with a +27 to hit did a pretty good job of taking him down while the wizard who was immune to lightning damage kept nailing him with chain lightning, not caring about the reflections.
When you get your skull-pieces put back together, *don't* ask me on which planet that was AL.