The Yoshi (ヨッシー) universe refers to the Super Smash Flash 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 symbol consists of a spotted Yoshi Egg rather than the iconic image of a Super Mushroom held by other Mario characters.
By 1990, Nintendo had established a hugely successful Mario video game franchise in a trio of NES platforming titles named Super Mario Bros., featuring Mario as a main character. Nintendo released the SNES in 1991, and Shigeru Miyamoto developed the platformer Super Mario World as a launch title. Graphics designer Shigefumi Hino, who would later direct Pikmin, created the dinosauric character Yoshi and had him and the rest of his multi-colored species introduced into the Mario universe through Super Mario World because Nintendo's design staff expressed a desire to see Mario ride a dinosaur. Yoshi was instantly popular with players and soon afterwards became the protagonist of his own series of platform and puzzle games for various consoles, as well as appearing frequently in many Mario games as a co-character.
Yoshi was made the main character of his own sub-universe with the release of the 1995 SNES sequel Super Mario World 2: Yoshi's Island, which introduced characters like Baby Mario and enemies like Raphael Raven, and the further sequel Yoshi's Story for N64 introduced a more saccharine atmosphere to the sub-universe along with more original characters like Pak E. Derm. Other games in which Yoshi has had a starring role include the puzzle games Yoshi's Egg, Yoshi, Tetris Attack, and Yoshi's Touch & Go!. A sequel to Yoshi's Island called Yoshi's Island DS was released for the DS in 2006, with more playable characters and the same art design. After that, the Yoshi series remained dormant for eight years, that would come to an end with the release of Yoshi's New Island for the 3DS, which is also a sequel to Yoshi's Island and its story picks right immediately after the end of the first game. Yoshi's Woolly World, the first Yoshi game developed for a Nintendo home console in eighteen years, would come to the Wii U in 2015. It is ambiented in a world where everything is completely made of yarn and other knitting stuff. The game was so anticipated, in fact, that Super Smash Bros. for Wii U managed to include a stage based on Yoshi's Woolly World, almost year before the release of the actual game.
The Yoshi sub-franchise is essentially the division of the main Mario franchise that focuses on being especially bright and cheery, and in various cases Yoshi-centric games are oriented more towards young gamers than the general Mario games. Yoshi itself is a frequently recurring character in many of the Mario games, however, and is practically a staple character in games where many Mario characters are available for selection, such as all of the Mario Kart series, the Mario Sports series such as Golf and Tennis, and the Mario Party series. For his repeated involvement in this multitude of Mario titles, Yoshi has become a major character in the Mario universe.
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In the Super Smash Flash series
In Super Smash Flash 2
After being left out from Super Smash Flash, the Yoshi universe is presented in Super Smash Flash 2 only about as big as most of the other franchises represented in the game, with one character and three stages represented (for the moment), and there is no item that can be considered Yoshi-centric.
The following character is considered both part of his own universe and part of the "Marioverse".
Yoshi: A multicolored species of bright, optimistic asexual dinosaur first seen as a mount for Mario in Super Mario World. One particular green Yoshi, who the name Yoshi is often used to refer to, is often a co-star in many Mario games, and it has also been made as the star of many of its own games, often platformers and puzzle games. Yoshi are used as a mode of transportation by Mario at times, and in other cases. All colored species of Yoshi have the ability to swallow up enemies with their stretchable tongues and eject them as Yoshi eggs, which the Yoshi can find various uses for such as throwing the eggs as projectiles. Yoshi are also able to hover in air momentarily. These abilities are directly reflected in Yoshi's appearance as a fighter; however, it is one of two fighters not to have a third jump in its B-Up move, which is considered a major disadvantage. Yoshi's Final Smash is Super Dragon. Yoshi grows wings, which allow him to fly around the stage and shoot fireballs.
As of now, 3 stages appear in the game, two based on the stages in the original Super Smash Bros. games and one that was custom-made.
Yoshi's Island: An original looking stage, with a big fortune of wheel-like in the center of the stage, the stage hovers in front of the actual island. Some Goonies fly by, and can be used as platforms as they fly around.
Yoshi's Island (64): From Super Smash Bros., a very colorful stage that looks like a pop-out children book. It has the Super Happy Tree in background behind the platforms and clouds that can also be used as platforms but fade away if stood for too long.
Yoshi's Story: From Super Smash Bros. Melee, a somewhat simplistic stage based on Yoshi's Story, featuring Propeller Shy Guys carrying food flying through the stage and Pak E. Derm being in the background. There is a cloud in the bottom who travels on a rail and it will take anybody who stands on it, before it hides on the sides of the stage, to come out on the opposite side.