For the Boss versions of Rootmars, see Rootmars.
In Metal Slug 6, at the end of Mission 2, Morden explains to Marco and his team what happened several weeks ago. In the flashback, at the bottom of the screen (below Morden and his tank), Rootmars' brain is shown, having been recovered from the depths of the ocean.
As Rootmars lay dormant under the sea, the Martians were left defenseless against their natural predators, the Invaders, who took the opportunity to conquer both the Martians and Earth. With the help of the Rebel Army, the Martians rescued Rootmars and after some misunderstanding, allied themselves with the Regular Army to counter the Invaders. If the player rides Rootmars in the 4th mission, then it — instead of Morden — will appear to rescue the players at the end of the final mission.
In Mission 4, near the end of the first area, if the players head below on the highway, the laugh of Rootmars cackles and it grabs them, taking the role of a Slug (the upper road lets the players use the Slug Flyer). It has a 360-degree 10mm vulcan and an electric brainwave (usable via the Bomb/Cannon Button), but doesn't offer protection to the players. To avoid damage during the ride, the players are required to press up and down on the D-pad, which changes the position of Rootmars' arms. Graphically, Rootmars has his dome-like helmet back in Metal Slug 6 to prevent further damage like in Metal Slug 3, his only weak spot, and he no longer has any stitches on his face.
- Rootmars is the only boss that can be used as a slug.
- Rootmars is the second toughest unit in Metal Slug Defense , with 30,000 HP at level 30. He is also the most expensive unit to buy and deploy. He cost 500 medals and he needs 999 AP to be deployed in battle.
- He returns on Metal Slug Attack as a "Pack Shop Unit" for the New Year's Celebration. His base AP cost (on iron tier) is the highest at the date, being 3000 (1000 on Platinum). Also, received a counter attack in case to be impacted by an enemy shoot or smash.
|Mechanized||SV-001 (Metal Slug) | SV-001 Type-R | Slug Copter | Slug Flyer | Slug Sub | Astro Slug | Slug Gunner | Slugnoid | LV Armor | Walking Machine | Slug Mariner | Drill Slug | M-15A Bradley | Metal Claw | Forklift | Slug Mobile | Augensterm | Protogunner | Slug Digger | Slug Trolley | Slug Armor | Slug Gigant | Golden Slug | MS-Alice | Ball Slug|
|Animal||SV-Camel | Elephant Slug | Ostrich Slug | Donkey Slug|
|Other||Middle-Son 1986 | Middle-Son 1999 | SV-002 | Borobune Slug | Motorcycle | Regular Army Helicopter | Landseek | PA33-21 Boat | RA-TTT | Rootmars|