Perspective: Side view
Visual: 2D scrolling
Gameplay: Arcade, Platform, Shooter
Published by: SNK Playmore Corporation
Developed by: SNK Playmore Corporation
Metal Slug 6 returns to the Rebel-Martian alliance shown in Metal Slug 2 and 3, but on a larger scale. Unlike the named games in which the Martians betray the rebels and they join the player in turn, both factions join the player due to a greater threat, later the Martians and the rebel soldiers would join again.
There are two modes that can be chosen at the beginning of the game: Easy and Hard. The easy mode reduces the difficulty of the game and changes the player's main weapon for a Heavy Machine Gun (heavy machine gun, with infinite ammunition); however, the game ends before the fifth and final mission.
In turn, in this game new vehicles are added (Donkey Slug a donkey to which a cannon can be attached, being able to reach higher places; Slug Digger, Slug Gunner and the Slug Gunner Prototype), as well as new weapons, the Zantetsu Sword [Z], which is a melee weapon that emits great energy and can neutralize enemy attacks. The ability to own two weapons is also added, for which one more button is added.
At the end of mission 4 you can take an alternate route where you can ride rootmars (Metal Slug 3's final boss) instead of the Slug Flyer. By choosing that route, after defeating the final boss rootmars is the one who saves you instead of General Morden.
There are rumors that Morden is still alive and that he has reunited his old army. The regular army is sent to investigate. In parallel, a giant meteorite falls to the ground. The Peregrine Falcons confirm and advise the Sparrows and the Ikari Team that it is General Donald Morden. It is also discovered that it forms an underground base in the crater. He has brought together Ptololemaic technology, applied alien technology (Amadeus), SV001 and SV002 forming a devastating BOSS army.
In addition, he has again allied himself with the Martians, despite the fact that they had betrayed him 8 years before and kidnapped 6 years ago, spoiling their plans for world domination.
At the end of the second mission the player is captured again by the Martians who had done it in Metal Slug 3 in the last mission, but while the Martians and Morden are attacked by another race of aliens from the meteorite, the player manages to free themselves from the hoops that are thrown at him. A clip is shown of rebel soldiers pulling "Root Mars" out of the seabed with the help of the Martians because the leader of the Martians was defeated by the player long ago and Rootmars fell into the sea. They are also attacked before completely taking out "Root Mars". We also see that 2 of the new aliens arrive that take 2 Martians and eat them, another alien arrives and hits General Morden and he falls to the ground, and finally Rootmars, manages to get out of the sea, we do not return him Let's see, but until mission 4, when it seems that he captures the player but no, Rootmars helps the player to end the new alien threat, this time, Rootmars has 2 triggers on one side of his brain, with them you will shoot them at the new aliens, if much more things get close, use their brain waves to kill them easily, but try not to use it so much.
In each previous version of the game he ended up facing an enemy of a certain level of technology, resistance, strategic positions, crossfire, ambushes and mission chases. In Metal Slug 6 the player will face at all levels plus a new attack mode that is mass, at the same time.
There will be no alliances this time to defend the planet, except for the last missions, because by this point between the Sparrows and mostly by the new aliens more than half of the regular and rebel army have been annihilated (not counting that the Martians of Mars People panic at the presence of the new aliens and are paralyzed.) We see that in the last mission the rebel soldiers join the player, to help him end the new race of aliens, then the Martians are taken prisoner by the aliens and the player frees them one by one, at the end you will face the leader of the new aliens, a gigantic gray and black monster with a skull face and huge teeth; it breaks floors with bluish energy.