


The Angry Birds series has a couple of these.

All Star Fighters is a crossover of the various games made by D3 Publisher from its Simple series of budget games, of which the most notable include the Onechanbara series and Earth Defense Force series.The Atari Jaguar game and the two PC games are considered classics in the FPS genre. However, the most notable crossover is with the game Phantom of the Kill as not only they frequently collab with each other, but also they were published by the same company that published them, Fuji Games for Japanese version while Gumi Inc. Alchemist Code has a lot of collaborations and crossovers with famous series such as Fate/stay night, Disgaea, Fullmetal Alchemist (2003) and so on.Also, AdventureQuest and WarpForce are in the same period of time, but it began with a crossover from AdventureQuest.Before that, DragonFable and AdventureQuest had a crossover mission.Heroes and villains from all three have been featured in the game, although arguably the most evil villain of all three gets killed off right in the beginning of the game. AdventureQuest Worlds itself is one huge mix of the three main AE games, AdventureQuest, DragonFable, and MechQuest.AdventureQuest Worlds has a crossover event with Ctrl+Alt+Del.7.62 High Caliber has a mod named Blue Sun, which turns the native game in a cross-over with Jagged Alliance 2 note 7.62 High Caliber being the official sequel of Brigade E5: New Jagged Union, Creator-Driven Successor to the Jagged Alliance series: there are dialog lines mentionning the country Arulco ( 7.62 High Caliber being set in another Banana Republic suffering from a civil war), several dozen of mercenaries from the Jagged Alliance series can be hired, the weaponseller Bobby Ray can be contacted by radio, a sidequest involves Elliot who fled Arulco to escape from Deidrenna's constant brutality, etc.
