Sega

Sega Games Co., Ltd. (also referred to and stylized as SEGA) is a Japanese video game developer and publisher, headquartered in Tokyo, Japan. Starting as an arcade-focused company, SEGA moved into the game console market in the early 1980s with the SG-1000, later releasing now-iconic platforms such as the Sega Genesis (Known as the Mega Drive in Japan and European regions) and Sega Saturn. After a string of commercial failures and profit losses in the later half of the 1990s, SEGA quit the home console business in 2001, moving on to become a software developer. SEGA is most known for their mascot, Sonic the Hedgehog, who debuted in 1991. The company is currently a subsidiary of Sega Sammy Holdings.

Rivalry
During SEGA's time in the console business, during the 8-bit and 16-bit eras, the company usually mocked Nintendo's properties in their games. In addition, marketing from the era usually portrayed SEGA's platforms as superior to Nintendo's, even going as far to mention the company by name. An early mockery toward Nintendo can be found in the final game of the Alex Kidd series, Alex Kidd in Shinobi World, where the first boss was originally going to be named Mari-Oh, an obvious parody of Mario. However, it was later changed to Kabuto. In the British  series from Fleetway, characters known as the Marxio Brothers appeared.

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, '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
SEGA's final console, the Dreamcast, was discontinued in 2001 in America and 2007 in Japan, after failing to rival consoles such as Sony's PlayStation 2.

 marked the first post-Sonic appearance of a SEGA game on a Nintendo console, specifically the Nintendo GameCube. Since then, both SEGA and Nintendo have collaborated on several projects. 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, 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 Olympic Games Tokyo 2020 - Nintendo Switch, 2019

Mario games published by Sega

 * VS. Super Mario Bros. (published by Sega, S.A. SONIC in several European countries)
 * 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 Olympic Games Tokyo 2020