Jetgoshi is the OC of the creator of the same name. His more recent appearance is essentially as green, anthropomorphic reptilian who acts and speaks like the average human does, but can also breathe fire and transform into a Charizard, while his former self was a similarly-dressed Yoshi lookalike under the alias of Cyber Yoshi.
As mentioned above, Jetgoshi used to be of a similar appearance to the cutesy green dinosaur from the Super Mario series. Though there wasn't much of a backstory to him way back when, he appeared to have an arch-nemesis known as Mecha Yoshi, who (as his name suggests) was a mechanised version of Jetgoshi (or more fittingly, Cyber Yoshi). His newer (or "modern") appearance does have a backstory, which revolves around his quest to defeat the evil Tyrantron and his evil forces with the help of his friends, Konlin Mae Kowan and Kelly.
In M.U.G.E.N, both old and new versions of Jetgoshi have been created by Jetgoshi himself.
Jetgoshi (Cyber Yoshi)
This is the first version of Jetgoshi under the nickname of "Cyber Yoshi". His basic moves are similar to that of Claymizer's Blaziken, as he was used as a base. An update changed his moveset to make him play as if he weren't a spriteswap, made him compatible with most fatalities, and balanced his stat placements and attack damages.
Jetgoshi (Modern/Lizard version)
The newest version of Jetgoshi is based off his modern look, and it used the Eoh MvC template by Acey. He was created without spriteswapping, and can rival characters from M.U.G.E.N game, DC vs Marvel. He uses various voice clips of Deadpool from MvC3.