New Slugs
The Metal Slug, Type-R Metal Slug, Slug Flyer and a Slug Gunner prototype make an appearance in the game, as well as some new ones.
Roba Slug: A donkey with a mounted vulcan cannon. Like all Animal Slugs, the donkey provides no protection to the rider. Later on in the level, the Donkey Slug acquires a two-wheeled out-house cart mounted with a Metal Slug cannon that replaces the player's grenade with Metal Slug cannon shots. It can also serve as a platform.
Mister Slug: Also called Slug Drilled. A multi-purpose subterranean digger as well as a helicopter. It has retractable drills on the left, right, and bottom sides, which are used to drill into the earth, and sports two vulcan cannons, which can also be used to drill through things by firing bullets into the dirt. The players cannot get out of the Slug, neither can they perform the Metal Slug attack with it. If the Slug Digger is destroyed, the player is killed. Its cannon shot is a mine that stays in place until an enemy touches it or it is shot.
Proto Gunner: It is similar to the Slug Gunner from MS5, but it has no melee attack, it does not have tank mode, and the player is exposed to enemy attacks. Its vulcan cannon is more like that of the Metal Slug and it has vulcan fix system.
Rootmars: Previously the final boss in MS3. The cannon is a shockwave coming from Rootmarks's brain which kills all enemies. If the player rides him, in the ending he, instead of Morden, saves the player.
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