http://pokemonshowdown.com/replay/ou-90628097 — Life Orb Celebi with Swords Dance/Seed Bomb/Zen Headbutt/Sucker Punch is a very reliable cleaner.
More relevant to the topic at hand:
>Leaving Landorus-T in on an Air Balloon Aegislash. If it's an Aegislash with an Air Balloon, it's pretty obvious you're about to eat a Hidden Power Ice.
>Leaving Mega Charizard X in to take Toxic damage. When Charizard had never even set up and thus had no reason not to switch.
>Leaving Latias in after the Draco Meteor nerf.
>Draco Meteoring my Blissey instead of just whacking me with Psyshock.
Another match, I think Celebi actually ended up taking out five of my opponent's Pokémon.