Super Devil is a special mode (and rank) where you can play as any character with green skin and powerful weapons.
The Super Devil is an unknown entity who possesses greater strength than the most established of armies. People who come in contact with the Super Devil will go extremely head over heels towards the devil. The Super Devil is benevolent enough to provide services to the Regular Army in times of high crisis.
The Super Devil has no physical appearance, but its able to possess soldiers to communicate and attack. A possessed soldier has green skin, glowing red eyes, and a serious demeanor on one's face. Often a person seeing a Super Devil will happily ignore the hapless soldier. Mortal entities were able to harness the Super Devil's powers and use them to their advantage. Likewise, the powers of a Super Devil can be reverted through the use of a vial.
In the Metal Slug universe, a Super Devil is the highest rank in the military surpassing the General of the Army. Reaching this rank grants the player with extra bonuses.
In the game's respective Combat School, having the fastest runs in Pin Point and beating Survival Mode will net the player with the max score of 1,000 points. Reaching this amount raises the rank ladder from "General of the Army" to "Super Devil" (this rank is hidden when below one thousand points).
When in Survival Mode, the player character appears with green skin (sometimes purple skin). Their default pistol is changed to shoot powerful Slug Cannons (or Super Grenades in MSX). While this eases the difficulty, the player character still dies in one hit resulting in a complete restart. Collecting any special weapon replaces the Super Devil pistol, a problem since the special weapons have infinite ammo in Survival Mode. Players also keep their weapon in transitioning to the next stage. Becoming a mummy reverts the Super Devil pistol to a standard pistol.
Super Devil Mode is only available to the profiles that have the rank. There is no way to revert to standard Survival Mode unless a new profile is made.
Collecting 23 Rank Medals in Very Hard difficulty awards the player with the Super Devil (SD) rank. The player is given invulnerability for the rest of the game, the exceptions are being crushed, falling in a pit, or landing on spikes. The only way to turn Super Devil Mode off is to start the game from the beginning as selecting S-Continue keeps the rank.
Rescuing all one hundred prisoners awards the player with the Super Devil (SD) rank. As a bonus, pressing down at the character select screen unlocks Hero Mode. In this mode, the player characters ditch their guns for powerful punching gloves that are able to knock out almost everything in one swing and gain the ability to throw infinite grenades. As a compromise, they also die in one hit, costing a retry.
Hyakutaro is ranked as a Super Devil in this game; he's ranked as a Second Lieutenant in every other game.
S-Ranking all Combat School missions nets the player with the max amount of 10,000 points. This changes the player's rank from GA to GS. When in Survival Mode, a red Mobile Satellite hovers over the player. The Red MOBS has infinite ion bolts. Collecting a weapon causes the MOBS to self destruct, and it cannot be brought back unless the player restarts the mission again.
Despite the player's choice when hitting the GA rank (becoming Cynthia's spouse or drill instructor), Cynthia instantly denies she had any sort of relationship when the Super Devil shows up.
Super Devil versions of Marco, Tarma, Eri, and Fio appear as purchasable units when the player hits 10,000 points on the Co-Op Ranking Event. A Super Devil unit's weapon is the Slug Cannon, and the unit charges forward in a barrage of shots for its special attack. Each Super Devil costs 10,000 points, needs 999 AP to deploy, and has 2,500 HP at level 1 (going up to a maximum of 12,500 at level 40). Unlike other units, only one Super Devil can be placed in a deck at a time.
The Super Devil this time becomes an online rank in the game, being the highest ranking which requires a total of 3,000,000 points or above to get this rank. The Super Devil rank doesn't have any physical changes or attributes to any of the units in the game.
Super Devil units became available starting with the "Green Monster" event. Unlike in Metal Slug Defense, each unit has their own ways of attacking, and all Super Devil units can be placed in a deck. The events' cutscenes also show the different manners in which a character becomes a Super Devil.
- Super Devil Eri is a pre-acquisition unit for the "Green Monster" event. She replaces her Slug Cannons with Hand Piercers that travel at a very long distance. In the event's opening cutscene, Eri transformed into a Super Devil after a green Hazmat Soldier rolled a bowling ball grenade at her.
- Super Devil Marco is a pre-acquisition unit for the "Maximum Evolution" event. He no longer charges forward when firing his Slug Cannons. Marco transformed into a Super Devil when a stray bat dropped a cauldron on him. He returned to normal after another bat dropped a vial on him.
- Super Devil Tarma is a pre-acquisition unit for the "Last Resort" event. He plays the same way as he did in Metal Slug Defense. Tarma was possessed by the Super Devil. He returned to normal after the Super Devil completed its task.
It's revealed that the Super Devil is apparently an entity of some sort, as Sophia states that it only comes when a crisis is about to hit the Regular Army.
- Sophia can be seen wearing a devil outfit in Metal Slug's concept art.
- Margaret refers to her students as "Greenhorns" (a novice), which the Super Devil has in its insignia.
- Touching Margaret's chest in Metal Slug Defense in any other rank causes her to berate the player. As a Super Devil, she sees this as a form of flirting.