Metal Slug X is a game in which players fight numerous enemies using different weapons, including the Metal Slug tank. The game is divided into levels; at the end of each is a boss that must also be defeated in order for players to advance to the next level. In each level, players will chance upon weapon upgrades and Metal Slug tanks. The tanks can be used for more defense and attacking power. In addition to upgrades, players will also encounter prisoners of war who, when freed, may give out bonuses such as weapons and random items. Apart from shooting, players can also use other moves and weapons to defeat enemies.
In Metal Slug X, players can first go through Combat School where they can test their skills while starting the main mission. Players earn scores based on the number of enemies defeated as well as the number of prisoners of war freed. To help players finish levels and defeat enemies, the game provides four devices. Aside from the tank, players are also given a Slugnoid, which is a mechanical jumping apparatus, a jet, and a camel that can help carry artillery. Weapons available to the player include a flameshot, a heavy machine gun, a rocket launcher, a laser rifle, a super grenade, and an iron lizard.