An enhanced version of Metal Slug 2, titled Metal Slug X, was released in March 1999 for the Neo Geo MVS. It fixed problems slowing the original game, and increased the difficulty. Metal Slug X also introduced some new elements into the game system.
Much of the music has been remixed or altered. Many stages have the time of day changed. Instead of individual levels that are set in any day or night, the stages can take place at dusk, twilight, or sunset. It is now possible for the player character to become fat by collecting food at all stages after Mission 2 , in the original game , the obese transformation was only possible in Mission 4 . All levels contain an increased enemy count and new enemy placements, and different enemy characters, and new key placements. Types and locations of vehicles are different.
There are more power- ups, prisoners of war and the elements (especially food) in each mission. These elements are often hidden.
Many of the elements of the environment have different reactions when fired, as the explosion of unexpected results or spitting random items or enemies. Stronger versions, such as the heavy machine gun, flameshot, shotgun, laser rifle, and rocket launcher are available. Each deals more damage than its normal counterpart, has a different appearance and a wider (or more) impact area. If the player happens to be fat while using these heavier weapons, which appear differently and can cause even more damage. Several new weapons include: Stones, Iron Lizard, Enemy Chaser, Super Granada, Drop Shot and a new Metal Slug gold, which is available in Mission 3. The original art for Metal Slug will show at the end of the game while the credits are rolling, instead of the black screen used in Metal Slug 2.