Metal Slug XX

Metal Slug XX is a revised version of Metal Slug 7 released in 2009 in Japan and in 2010 in North America by Atlus for the PlayStation Portable. This version features additional content, including co-op multiplayer and Leona Heidern as a downloadable content.

Metal Slug XX was also released on Xbox Live Arcade in 2010 and was made backwards compatible on Xbox One in 2016. A remastered version for the PlayStation 4 and Microsoft Windows (Steam) was released in May 29, 2018.

Characters
The game has the same set of characters in Metal Slug 6 with the same abilities as its predecessor:

PlayStation Portable

 * The screen and graphics are not re-dimensioned anymore, like in the Nintendo DS. Additionally, the player can select the aspect ratio of the screen:
 * 4:3 (Regular aspect ratio with designed borders at left and right of the screen)
 * Wide (Fullscreen with the graphics stretched)
 * Clear (Classic Neo Geo aspect ratio)
 * Rebel Troops reuse their sound effects from Metal Slug 6 (except for Xbox 360/One).
 * Old enemies reappear again such as the Mars People and the Hunters.
 * Change in items, Slugs, and enemy placement. The Ostrich Slug is added in this version.
 * Mission 1 and Mission 6 take place in different times of day.
 * Infinite continues to all difficulties.
 * A new announcer; bits and pieces of the previous announcers can be heard.
 * Reintrodution of multiplayer mode by using ad hoc and online services. Unlike previous games, there is no drop-in multiplayer.
 * Leona Heidern as a downloadable character (costs $0.99). She has several gameplay benefits:
 * Her Special Action is the Moon Slasher. It can tear down enemies and machinery with higher damage than grenades. It can also nullify projectiles.
 * Vehicle Slugs' health is increased from three to four hits.
 * 20% more ammo on any weapon crate.
 * 20% more grenades/firebomb. Leona's grenades are her earring bombs.
 * Leona keeps her weapons upon death. She loses them when continuing.
 * Altered challenges and ranking table in the Combat School mode. The Item Collection challenges are replaced by the returning Survival challenge and Super Devil rank. Players can switch characters without quitting back to the challenge list.
 * Implementation of Hidden Routes:
 * Mission 1
 * Hunter Hideaway: There should be a pitfall/hole before the Di-Cokka and the DANGER barrel. Go there and fight the Hunters.
 * Mission 5:
 * Deeper Ruins: When you reach the end of the second part of the stage, it says GO right. Instead, go left until you find a Warp Base. Get in the Base and fight UFOs and tons of soldiers.
 * Mars People Hallway: Just like the previous entrance but do not go in the Base. Jump over it. You should fight hordes of Mars People in there.

Xbox 360/Xbox One:

 * Achievements (12)
 * Sound Adjustments:
 * Leona uses a unique death cry rather than using her old King Of Fighters defeat sound.
 * The Rebels use their old Neo Geo yells.
 * The new announcer shouts "Final Mission Start" instead of the Metal Slug 6 announcer.

PlayStation 4/Steam:

 * Leona Heidern available from the get-go (no purchase required).
 * 4K and 1080p resolution. The characters in the menu screen have been redrawn.
 * New borders for the Clear and 4:3 aspect ratios.
 * Scanlines to simulate CRT and Arcade screens.
 * PlayStation trophy support (30 including a Platinum).
 * Steam achievements (34).

Trivia

 * This game, Metal Slug 6, Metal Slug 7 and Metal Slug Defense are the only game of the series to receive characters from the other franchises, whether from the company itself or from other companies.
 * This makes the game, along with Samurai Shodown (2019), Art of Fighting 2 and Fatal Fury Special the only non-crossover games to receive characters from the other franchises.