An item associated with the Super Smash Bros. franchise. It is simply a white letter with the Super Smash Bros. logo as a red wax seal.
It originally appeared in the first trailer for Super Smash Bros. for WiiU/Nintendo 3DS as a letter of invitation only extended to the Villager of Animal Crossing, as a play on that game's letter system. Thanks to fan popularity, the invitation was used in association with other hopefuls and eventual roster entries.