The Yoshi universe, sometimes known as the Yoshi's Island universe, (ヨッシー, Yoshi) refers to the Smash Bros. series' collection of characters, stages, and properties that hail from the sub-franchise of the Mario series that deals with main sub-series character Yoshi. It is generally agreed on that Yoshi and related items count as Mario properties, but Yoshi has appeared in enough of his own games alongside enough original characters and properties that many consider him as holding sway over a "sub-universe" of Mario. Yoshi is also considered part of his own universe because his smasher's insignia consists of a spotted Yoshi Egg rather than the iconic image of a Super Mushroom held by other Mario characters. It is the least representative of the Mario sub-series, since there is only one character, two or more stages, but no items or no Assist Trophies.
Throughout the lifepsan of the Famicom / NES, Shigeru Miyamoto wanted Mario to have a dinosaur companion in his games following Super Mario Bros., but apparently, limitations to the NES could not fit this companion character in. However, Miyamoto was able to achieve the debut of the character, Yoshi, in the Super Famicom/SNES launch game Super Mario World. Yoshi was designed by the game's graphics designer Shigefumi Hino (who would become famous later on as the designer of the Pikmin series), and was introduced as a species of human-sized cartoon-like dinosaurs that came in multiple different colors, could swallow enemies with their elastic tongues, could lay spotted eggs that usually hatched into power-ups, and could be ridden by Mario through levels as a mount. The Yoshi species became a permanent, recurring element in the Mario franchise forever onward, and any reference to "Yoshi" as a character typically refers to a green-colored individual that is one of the recurring heroes in Mario's world.
Yoshi, whether the character himself or the species, has appeared in a "primary side-role" alongside various other Mario-series regulars in many Mario games, oftentimes as a selectable playable character; games involving Mario where Yoshi may be selected include the Mario Kart sub-series, as a recurring racer, and the Mario Party sub-series, as a recurring character choice for walking across the board and partaking in mini-games. More significantly, there have been occasional games starring Yoshi in a leading role, with or without Mario in a side-role; aside from several occasional puzzle games, including Tetris Attack on the SNES, Yoshi's first high-profile starring role was in the very well-received and successful Super Mario World 2: Yoshi's Island for the SNES in 1995, several years after Yoshi's debut. In this game, Yoshi and his differently-colored friends, illustrated in a unique pastel style to help differentiate the game from the CGI imagery of Donkey Kong Country, help transport a baby version of Mario through their island's obstacles to reunite him with his brother and bring them back to the stork that is supposed to deliver them to their parents. A spiritual sequel focusing exclusively on the Yoshis, Yoshi's Story for the Nintendo 64 in March 1998, featured a more saccharine aesthetic; by this point, Yoshi had settled into a different design that gave him a more anthropomorphic appearance, which has been used ever since.
Despite the close association Yoshi's modern design has with the Yoshi's Story aesthetic, that aesthetic actually never made a reappearance in a Yoshi-centric title, whereas the pastel design style of Yoshi's Island for the SNES has been reused in several later-generation follow-ups. These may be referred to as part of the "main" Yoshi series, the "Yoshi's Island" sub-series, where Yoshi has to navigate platforming stages and attack foes with his eggs in order to transport Baby Mario and baby versions of other characters safely to the end. Aside from Yoshi Touch & Go for the DS, which appears to not even have any canonical relevance to the overall Mario franchise despite a similar scenario focused on transporting Baby Mario, there have been two direct sequels using the pastel aesthetic: Yoshi's Island DS, released for the Nintendo DS in November 2006, Yoshi's New Island, released in 2014 on the Nintendo 3DS, and the newest game, Yoshi's Wooly World. Between these games and Yoshi's constant appearances in most Mario games, Yoshi has been enough of a recurring Nintendo character that the Super Smash Bros. series of fighting games not only included him as a regular playable character since the series' start, but saw fit to symbolically categorize Yoshi and related properties as "separate" from the Mario universe, the same way Donkey Kong and Wario have been categorized as "separate franchises" from Mario.
In Super Smash Bros.
If treated separately from the Mario universe, the Yoshi universe is only about as big as most of the other franchises represented in SSB, with one character and one stage represented, and there is no item that can be considered Yoshi-centric.
The character Yoshi is considered both part of his own universe and part of the Mario Universe.
If the Yoshi universe is counted as separate from the rest of the Mario universe, Super Smash Bros. features one Yoshi-themed stage:
In Super Smash Bros. Melee
While Melee is much bigger than Super Smash Bros., none of the game's items are based on Yoshi save for the Yoshi's Egg item which was only used in an Event Match, There is only one character, two new stages along with Yoshi's Island returning from the previous game, and a wide variety of new Trophies.
Full Trophy List
In Super Smash Bros. Brawl
The Yoshi universe receives representation in Super Smash Bros. Brawl.
On the final character select screen (after all characters are unlocked), Yoshi, despite being part of the Original 8, doesn't appear in the top row in the spot between Samus and Kirby. Instead, he shares a column with fellow Mario side series characters Donkey Kong, Diddy Kong, and Wario.
Once again, the Yoshi series is represented in both versions by a character and several stages, one new and two returning from past installments. The series is now referred to as the Yoshi's Island series in at least Super Smash Bros. for Nintendo 3DS.
Main article: List of SSB4 trophies (Yoshi's Island series)
These are all of the known trophies from the Yoshi series.
Games with elements in the Smash Bros. games
Technically, Super Mario World qualifies as part of the Mario universe due to it being a main series Mario game. However, the Smash Bros. games consider it part of the Yoshi universe as well, with it being Yoshi's debut appearance and one of his most iconic.
In Super Smash Bros. Melee, the Yoshi's Island stage is based on Super Mario World and is clearly labeled as such in Brawl and Super Smash Bros. for Wii U. A few of Yoshi's moves in all four Smash Bros. games are also based off of what he could do in this game. In Super Smash Bros. Brawl, Yoshi's Final Smash, Super Dragon, is based on the powers he could obtain in this game, specifically the powers gained from a red Koopa, which allows him to breathe fire and a blue Koopa, which allows him to sprout wings and fly.
Yoshi's red, blue and yellow alternate costumes in Super Smash Bros. Melee, Super Smash Bros. Brawl and Super Smash Bros. for Nintendo 3DS / Wii U are based on those specific colored Yoshis in Super Mario World.
In Brawl, there is a stage called Yoshi's Island that is based on many elements from that game, such as the design of the stage (which looks similar to drawings) and the background characters. There are also some music tracks that come from the same game. They all play in this stage.
Yoshi's special moves, Egg Lay, Egg Throw and Yoshi Bomb come from this game. Yoshi's second jump (known as the Flutter Jump) originated from this game. His down aerial could also be a reference to his Flutter Jump ability. Also, Yoshi's pink, cyan and purple alternate costumes in Super Smash Bros. Brawl and Super Smash Bros. for Nintendo 3DS / Wii U are based on those specific colored Yoshis in Super Mario World 2: Yoshi's Island. Baby Mario and Kamek debuted in this game. Baby Mario appears as a trophy while Kamek appears on the Mushroom Kingdom U stage. Baby Mario also appears as three stickers in Super Smash Bros. Brawl, one in his Superstar form. Baby Luigi appears as a sticker, riding on Luigi, in their artwork for Mario & Luigi: Partners in Time in Super Smash Bros. Brawl and a trophy in Super Smash Bros. for Wii U. Stork, Goonie, Crayzee Dayzee, Fly Guy, Tap-Tap, Burt the Bashful, and Raphael the Raven all appear as stickers in Super Smash Bros. Brawl.
In Super Smash Bros., there is a stage called Yoshi's Island that was based on this game, featuring the Super Happy Tree and other characters from Yoshi's Story in the background, and a main platform resembling an opened book. This stage returned as a past stage in Melee. Yoshi's victory theme is an orchestration of the main theme and the "level complete" fanfare from this game.
In Melee, there is another stage based on Yoshi's Story, which is also named after it.
A remix of the game's ending theme is included in Brawl and SSB4 and plays on the new Yoshi's Island stage, which is based more on the Yoshi's Island franchise than Yoshi's Story. The music also appears on the stage Woolly World.
Yoshi's black alternate costume in Super Smash Bros. for Nintendo 3DS / Wii U is based on a black Yoshi in this game.
Yoshi's voice clips from all four games (five if one counts the 3DS and Wii U versions of SSB4 as different games) are from this game.
The game's "above ground" theme has been remixed and included in this game, and was given the title "Wildlands". The graphics of the stage Yoshi's Island is based on Yoshi's Island DS's graphics. Stork Stop appears as a sticker in Super Smash Bros. Brawl.