Metal Slug 3 is a run and gun video game for the Neo-Geo console/arcade platform created by SNK that was released in 2000 and is the sequel to Metal Slug 2. Being the last Metal Slug that SNK was working on until the bankruptcy, it was given a lot of features, enhancements and improvements. The music of the game was developed by Noise Factory. The game was ported to the PlayStation 2 and Xbox. The game was also released for the Wii, PSP, and PS2 as part of the Metal Slug Anthology.
The rebellion orchestrated by General Morden to bring about a new global regime is now ancient history, and order and peace has begun to return to the world. Morden, brought back into power, was attempting another coup d'état, but government forces got wind of the plot beforehand and pre-empted the impending assault.
Instrumental in squashing Morden's rebel forces, Marco and Tarma of the Peregrine Falcon Strike Force are ordered to lead the team after their earlier requests for resignation were denied. Although General Morden has been written off as "missing" by his followers, they have hidden themselves throughout the world, and Marco and Tarma's abilities and experience are seen as a necessity to destroy remaining rebel strongholds, one by one. Throughout the furious fighting against the holdouts, Marco and Tarma cannot help but suspect Morden's involvement in this new evil plan for world domination.
Meanwhile, the SPARROWS, a special strike force within the government intelligence agency, have come across a series of strange events running parallel to the Peregrine's pursuit of General Morden. From trivial abductions of livestock to the disappearance of government officials and the appearance of freakishly large creatures, numerous occurrences with nothing in common point to one grim possibility. General Morden is not the only menace to worry about. Eventually it is learned that the alien menace that appeared in Metal Slug 2/Metal Slug X have returned. After defeating what appears to be General Morden, it turns to really be an alien in disguise, while the real Morden was their prisoner (again). The aliens abduct the character the player uses, and another character takes his/her place. Once again, an ad-hoc alliance is formed to combat the external threat, with Rebel Army supplying a rocket ship that allows the player to break into the aliens' mothership. After a long battle throughout the ship's interior, mothership starts to collapse from all the damage. The player manages to escape, but is confronted by the aliens' leader, Rootmars, when falling through the Earth's atmosphere. Rootmars is defeated and is left for dead in the ocean.