Smash Bros. Countdown
The Smash Bros. Countdown was an event hosted by the Japanese Super Smash Bros. Twitter account, @SmashBrosJP, which featured other promotional Twitter accounts counting down to the release date of Super Smash Bros. Ultimate. The event started on November 27th, 2018, ten days away from the game's release date, and lasted up until the actual release date, December 7th.
In total, 22 accounts (including @SmashBrosJP itself) were involved in the event, and each posted a piece of promotional material, such as a screenshot or an illustration. The concept is similar to the character posters from the previous game, which featured franchise artists illustrating pieces for Smash Bros.; however, the countdown was not limited to newcomers, unlike the posters.
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The Smash Bros. contribution is a simple, minimalist image to introduce the concept.
The Super Mario Odyssey contribution is a short animated video. It features Cappy and Mario, in the form of the number 10, bouncing on-screen. The camera zooms in to reveal Mario, similar to the E3 2017 trailer for Super Mario Odyssey, as well as resembling the short countdown animations made for that game's release; however, he assumes his pose from the game's box art, which then transitions into the box art itself. This video was also reposted by @SuperMario_UK, the official European Mario account.
9 Days Left
8 Days Left
The Animal Crossing contribution is an illustration of Villager and Isabelle leaving their village, with Tutu, Sandy, Cesar, Genji, Nibbles, Ribbot, Rover, Pelly, Phyllis, and Pete looking on as they depart. This illustration was later reposted to the English language Animal Crossing accounts, @animalcrossing and @AC_Isabelle.
7 Days Left
The Bomberman contribution is an image of Bomberman running from an explosion.
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The Xenoblade contribution is a screenshot of Zeke, a playable character in Xenoblade Chronicles 2, saying "6 days to go, chums!" This screenshot was coupled with the announcement of an update to Xenoblade Chronicles 2, which added Mythra's support spirit design in Super Smash Bros. Ultimate as an alternate costume. This costume is available by equipping a new item, the Massive Melee Aux Core.
5 Days Left
Their contribution is a collage of every Pokémon character in Ultimate, including those summoned through Poké Balls and Master Balls. This was also coupled with the announcement of the Partner Pikachu and Partner Eevee spirits from Pokémon: Let's Go, Pikachu! and Let's Go, Eevee!, which were added to the game post-launch.
4 Days Left
Their contribution is an illustration by Yusuke Nakano, character designer of the Zelda series, that features the playable Zelda characters reaching for the Triforce.
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The eighth day's participants were @FE_Heroes_JP, the official Fire Emblem Heroes account; @platinumgames_j, the official Platinum Games account; @FireEmblemJP, the official Fire Emblem series account; and @yoiko_minecraft, the official account for the YouTube comedy duo Yoiko, which comprises Japanese comedians Shinya Arino and Masaru Hamaguchi.
The Fire Emblem Heroes contribution is an illustration in that game's chibi style, featuring the playable characters and Assist Trophies battling on Castle Siege. Characters from the same universe are grouped together. In addition, Lucina and Chrom's poses are reminiscent of the boxart for Fire Emblem: Awakening. Smoke trails indicate that Corrin launched Feh, the mascot for the Order of Heroes. In the center of the image, an Orb is emblazoned with an inverted Smash logo, similar to a Fake Smash Ball. The emblem for the kingdom of Askr, where Fire Emblem Heroes takes place, also appears in the background.
The Fire Emblem contribution is a screenshot of the seven playable Fire Emblem characters at the time on Arena Ferox. This was coupled with the announcement of the relaunched Fire Emblem World website, a general information source for the Fire Emblem series.
As noted in their Tweet, Yoiko are not featured in the game itself; however, they had previously appeared at Japanese pre-release tournaments for Ultimate, and also announced that they would be streaming an official Let's Play of the game.
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The Metal Gear contribution is a render of Solid Snake (taken from Metal Gear Solid: The Legacy Collection).
The Kid Icarus contribution is a screenshot of Pit in his "peace sign" victory pose; it was coupled with the unveiling of the Pit (Victory) AR Card for Kid Icarus: Uprising, which had never been released previously.
1 Day Left
The Mega Man contribution is an illustration by Yuji Ishihara, character designer of Mega Man 11, featuring Mega Man in his Ultimate and Mega Man 11 designs.
The Splatoon contribution is an illustration of an orange Inkling girl on Battlefield, having painted the number 1 with orange ink. The Inkling has the Super Smash Bros. logo in her eye, as a callback to the reveal trailer for the game.
On launch day, @SmashBrosJP posted a collage of every playable character to celebrate the game's release.
Prior to the game's American release, Joker was announced as a DLC fighter for Ultimate at The Game Awards 2018. In tandem with the announcement, @p_kouhou (the official Persona account) posted an illustration of Joker by Shigenori Soejima, character designer of the Persona series.