Sega

Sega (also referred to as SEGA) is a Japanese video game company. Its mascot is Sonic the Hedgehog, having replaced Alex Kidd in 1991. In the past, Sega used to be the rival company of Nintendo. As such, both engaged in frequent bouts of competition.

Rivalry
An early mockery toward Nintendo happened in Alex Kidd's final game, Alex Kidd in Shinobi World, where the first boss was originally going to be named Mari-Oh, a parody of Mario. However, it was changed to Kabuto. There are also characters called the "Marxio Brothers" in a British comic called Sonic the Comic.

To counter these mockeries of Mario, Rare had Sonic make a "cameo appearance" in Donkey Kong Country 2: Diddy's Kong Quest. His shoes, as well as a weapon from a fellow platforming mascot rival, Earthworm Jim's blaster, are seen next to a trash can during Cranky Kong's contest labeled "No Hopers".

Another possible mockery is the inclusion of a blue and quick hedgehog (Sonic's qualities) enemy called Harry Hedgehog in the game Super Mario World 2: Yoshi's Island.

Move to software developer
Nintendo and Sega rivaled for about a decade, eventually leading to Sega discontinuing the Sega Dreamcast in 2001 for America, Canada in 2002, and in Japan in 2007, and Sega became a third-party developer in 2001.

Super Monkey Ball marked the first post-Sonic appearance of a Sega game on a Nintendo console, specifically the Nintendo GameCube. With that, the feud ended, and the two companies began collaborating. Their first effort resulted in F-Zero GX and AX. The two companies later teamed up to create a crossover game featuring both Mario and Sonic, Mario & Sonic at the Olympic Games, which generated the Mario & Sonic series. Sonic also appeared as a playable character in the Super Smash Bros. series. He appeared with another fellow Sega character, Bayonetta who has appeared in Super Smash Bros. for Nintendo 3DS / Wii U and Super Smash Bros. Ultimate. Joker, a character from Sega subsidiary Atlus, is also playable in Super Smash Bros. Ultimate as DLC. Aside from the Mario & Sonic series and the Super Smash Bros. series, Sonic has made cameo appearances in the Mario universe. By using a Sonic amiibo, players can unlock an outfit based on Sonic in Yoshi's Woolly World and Mario Kart 8 (and their respective ports), as well as in Super Mario Maker. Yoshi's Island Zone is a downloadable level in the Wii U version of Sonic Lost World which features Sonic in Yoshi's Island.

As a third party developer, Sega currently makes games for a variety of devices, ranging from video game consoles and handhelds to smartphones.

Mario games developed by Sega

 * Canceled Donkey Kong parking attendant arcade game
 * Mario & Sonic at the Olympic Games - Wii, 2007; Nintendo DS, 2008
 * Mario & Sonic at the Olympic Winter Games - Wii, 2009; Nintendo DS, 2009
 * Mario & Sonic at the London 2012 Olympic Games — Wii, 2011; Nintendo 3DS, 2012
 * Mario & Sonic at the Sochi 2014 Olympic Winter Games - Wii U, 2013
 * Mario & Sonic at the Rio 2016 Olympic Games - Wii U, 2016; Nintendo 3DS, 2016
 * Mario & Sonic at the Tokyo 2020 Olympic Games - Nintendo Switch, 2019

Mario games published by Sega

 * Mario & Sonic at the Olympic Games (in North America and Europe only)
 * Mario & Sonic at the Olympic Winter Games (in North America and Europe only)
 * Mario & Sonic at the London 2012 Olympic Games (in North America and Europe only)
 * Luigi's Mansion Arcade
 * Mario & Sonic at the Tokyo 2020 Olympic Games