The Smash invitation is an envelope stamped in wax with the Super Smash Bros. logo featured in promotional materials and character reveal trailers for Super Smash Bros. 4 and Super Smash Bros. Ultimate. It first appeared in Villager's reveal trailer for Super Smash Bros. 4 and has since appeared in multiple other Super Smash Bros. Ultimate character trailers.
The invitation first made an appearance in Villager's trailer. In it, he is seen taking the envelope out of his mailbox before running off. Interestingly, this is the only appearance of the Smash invitation in any Smash 4 character trailer. Due to this, it is likely based on the letters one can receive in the Animal Crossing series.
The Smash invitation is much more prevalent in promotion for Ultimate characters, especially within the trailers for DLC characters. It first appeared in Isabelle's trailer, in which Pete (a pelican mailman from the Animal Crossing universe) delivers one to her. This and Villager's reveal are the only two fighter reveal trailers in which the character receives the letter by physical post. Additionally, until Pyra and Mythra's trailer, letters in following trailers are shown to not be directed towards a specific character.
In Joker's first trailer, he is seen running through The Game Awards 2018 while his teammates comment on what he may be there for. Shortly, it is revealed that he arrived to steal a Smash invitation. It reappears at the beginning of Joker's second trailer. Following that, it makes an appearance in Terry's reveal trailer, parodying the Bernstein clan's invitations seen throughout The King of Fighters series. In it, multiple characters from The King of Fighters series attempt to grab it as it flies through the air, including Kyo Kusanagi, Ryo Sakazaki, Andy Bogard, Joe Higashi, Geese Howard, Nakoruru via her hawk Mamahaha, and Iori Yagami, before it lands on the ground, allowing Terry to take it. It makes another appearance in Byleth's reveal trailer, in which Sothis summons it to gift to the aforementioned fighter.
It also appears in Min Min's reveal trailer, where multiple ARMS characters, including Spring Man, Ribbon Girl, Ninjara, Twintelle, Master Mummy and Kid Cobra, fight over it until Min Min appears and takes it for herself. In Pyra & Mythra's trailer, Rex searches for Pyra and finds her standing on Final Destination; she apologizes for not telling him about where she'd gone and shows the envelope to him.
Steve is implied to have received an invitation in an article on the official Minecraft website, stating that Mojang Studios employee Per Landin encountered the letter at the front door of the Studio, addressed to Steve and Alex, and then proceeding to state that Steve and Alex have been invited to Super Smash Bros. Nevertheless, this article was written by management of the aforementioned website, and is not necessarily recognized as Super Smash Bros. canon, as far as that may exist.
Aside from character reveal trailers, the Smash invitation has also been used as a general motif for the game's downloadable content. This can be seen in the Japanese download card for the Fighters Pass Vol. 1 and Vol. 2, which features an image of a Smash invitation on its front. It is often used in relation to unrevealed downloadable characters, as can be seen in several Super Smash Bros. Ultimate presentations and information on the game's website pertaining to downloadable content. It was also used in the September 4, 2019 Nintendo Direct to represent the confirmation of additional downloadable fighters outside of the Fighters Pass Vol. 1, months later it was confirmed that there will be six more playable characters in the Fighters Pass Vol. 2, and each challenger pack makes use of the Smash invitation as a placeholder before the character is revealed.
Additionally, a physical stationery set designed after the Smash invitation is offered for sale on the Japanese My Nintendo website. It costs 400 platinum points and consists of three envelopes, three wax seals, and six sheets of notepaper. The set could be considered the closest "official" look at the contents of the invitation, and is designed such that the notepaper fits within the envelope when folded in half.
This physical stationary later became available for purchase on My Nintendo in the United States on January 14th, 2021.