Sega

Sega (officially capitalized 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.

History
An early mockery happened in Alex Kidd's final game, Alex Kidd in Shinobi World. The first boss was originally going to be named Mari-Oh, a parody of Mario. However, it was changed to Kabuto (this name was later used for a Pokémon). There are also characters called the "Marxio Brothers" in Sonic the Comic, a British comic.

To counter these mockeries of Mario, Rare had Sonic and Earthworm Jim make "cameo appearances" in Donkey Kong Country 2: Diddy's Kong Quest. Although they apparently join Cranky Kong's contest of collecting DK Coins, Sonic and Jim apparently do not succeed in getting many coins. Neither ranks third place, and the pair seems to have fled from Mushroom World. Sonic leaves his shoes behind upon departure, and Earthworm Jim leaves behind his blaster. Both items are put by a trash can and labeled "No Hopes." Another (possible) mockery is the Harry Hedgehog enemy in Super Mario World 2: Yoshi's Island. Its blue coloration and rather quick moving pace may have been a mockery of Sonic; however, this may have been a coincidence.

Move to Software Developer
This feud lasted for many years, until Sega became a third-party developer in 2002 with the closing of their console-producing division. Sonic Adventure 2: Battle, a port of Sonic Adventure 2 for the Dreamcast, marked the first 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 AX/GX. The two companies later teamed up to create a crossover game featuring both Mario and Sonic, Mario & Sonic at the Olympic Games, which generated three sequels: Mario & Sonic at the Olympic Winter Games, Mario & Sonic at the London 2012 Olympic Games, and Mario & Sonic at the Sochi 2014 Olympic Winter Games. Sonic also appeared as a playable character in Super Smash Bros. Brawl, being one of two characters (the other being Solid Snake from the Metal Gear franchise) in the game that did not come from a Nintendo-owned franchise. Additionally, Mario himself was going to appear in Sonic & Sega All-Stars Racing as a character exclusive to the Nintendo Wii version, but was taken out after Nintendo and Sega agreed that Mario/Sonic crossovers were best suited for the Olympic Games series, despite Sonic had appeared previously in Super Smash Bros. Brawl and is set to appear in Super Smash Bros. for Nintendo 3DS / Wii U.

Mario Games developed by Sega

 * 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 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)