It is All Thanks Day in Canterlot, and the Bearers of Harmony are invited to the Royal Palace for a banquet in their honor. Rainbow Dash and Pinkie Pie have a plan. They're going to prank Princess Celestia. Maybe her tongue will inflate to double its size, or maybe her horn will go limp, or maybe her fur will turn purple with yellow polkadots. Princess Celestia is always up for a good prank, right? And nothing could go wrong... right?