Metal Slug 2

The game added several new features to the gameplay of the original Metal Slug, such as new weapons, vehicles and the ability to transform the character. It received generally positive reviews and was followed by Metal Slug 3, released in 2000.

Gameplay in Metal Slug 2 is similar to the previous game; the player must shoot constantly at a continual stream of enemies in order to reach the end of each level. At this point, the player confronts a boss, who is usually considerably larger and tougher than regular enemies. On the way through each level, the player can find numerous weapon upgrades and "Metal Slug" tanks. The tank is known as the SV-001 ("SV" stands for Super Vehicle), which increases the player's offense and considerably adds to their defense. In addition to shooting, the player can perform melee attacks by using a knife and/or kicking. The player does not die by coming into contact with enemies, and correspondingly, many of the enemy troops have melee attacks. Much of the game's scenery is destructible, and occasionally, this reveals extra items or power-ups. During the course of a level, the player encounters prisoners of war (POWs), who, if freed, offer the player bonuses in the form of random items or weapons. At the end of each level, the player receives a scoring bonus based on the number of freed POWs. If the player dies before the end of the level, the tally of freed POWs reverts to zero. Metal Slug 2 introduces the ability for characters to transform during the course of the game. As well as doubling the number of available player characters from two to four, Metal Slug 2 introduces in-game characters to help the player in battle. The first is Hyakutaro Ichimonji, a prisoner who, when rescued, will fight alongside the player, throwing Hadouken balls at enemies, or roundhouse kicking them if they get within melee range. Another character is Sgt. Rumi Aikawa, an army supplier who lacks a sense of direction, earning her the title "The Wandering Ghost"; she carries a huge, overstuffed backpack and drops random items for the player to collect (more are dropped if the backpack is shot or cut).

Two years have passed since the end of Metal Slug, when Capt. Marco Rossi and Lt. Tarma Roving of Peregrine Falcon Strike Force defeated and killed the evil General Morden, who had staged a coup d'état against the worlds' governments. Various factions sympathetic to Morden have been in operation, but are considered insignificant. They have begun to act in unison, and army intelligence concludes that the only way this could happen is if Morden is still alive and is attempting a new coup. Rossi (now a Major) and Roving (now a Captain) are sent to once again battle Morden. They are accompanied by two members of the Intelligence Agency's Special Ops Squad S.P.A.R.R.O.W.S.; Sgt. Eri Kasamoto and Sgt. 1st Class Fiolina Germi. As the levels unfold, it is revealed that Morden has formed an alliance with aliens in an effort to facilitate his plans (the previous game ended with one of Morden's soldiers sending a paper airplane into outer space). In the final mission, however, the aliens turn on Morden, attacking his troops and taking him prisoner. An ad hoc alliance is formed between the Peregrine Falcon Strike Force and General Morden's army to combat the greater alien threat. After a long battle, they succeed in defeating the alien mother ship. As the ship explodes, Morden falls to the ground, strapped to a solid iron plate. While his soldiers celebrate his survival, the plate loses its balance and crushes him. The game ends with Rossi, Roving, Kasamoto and Germi celebrating their victory.

An upgraded version of Metal Slug 2, titled Metal Slug X, was released in March 1999 for the Neo Geo MVS. The game used a modified version of the engine from Metal Slug 3, which eliminated the slowdown problems of the original. In addition to increased difficulty, Metal Slug X introduced several changes to gameplay and presentation: Much of the music has been remixed or altered. A new announcer. Many stages have the time of day changed. Instead of individual levels being set at either 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 items in every stage after Mission 2; in the original game, the obese transformation was only possible in Mission 4. All levels have increased enemy count, new enemy placements, different enemy characters and new boss placements. Vehicle types and locations are different. There are more power-ups, POWs, and items (particularly food) in each mission. These items are often hidden. Many environmental elements have different reactions when shot, such as exploding with unexpected results or randomly spewing out items or enemies. Stronger versions of the heavy machine gun, flamethrower, shotgun, laser rifle, and rocket launcher are available. Each deals more damage than their normal counterpart, has a different appearance and a wider (or longer) area of impact. If the player happens to be fat while using these heavier weapons, they appear differently and can cause even more damage. Several new weapons are included: Stones, Iron Lizard, Enemy Chaser, Super Grenade, Drop Shot, a new Golden Metal Slug, which is available in Mission 3, and the Armor piercer, available in Mission 4. Added Fio's death sound (in Metal Slug 2, she uses Eri's). New enemies are added or replaced, like the Mummy Dogs. The original art for Metal Slug is shown at the end of the game while the credits are rolling, instead of the black screen used in Metal Slug 2.

Home versions of Metal Slug 2 were released for the Neo Geo AES in April 1998, and the Neo Geo CD in June. The Neo Geo CD version features a "Combat School" mode (similar to the CD-ROM based versions of the previous game) where the player can play new versions of previously played missions with new objectives. Metal Slug X was ported to the Neo Geo AES in May 1999 and the PlayStation in January 2001. The PlayStation version was released in North America and PAL regions by Agetec and features the same "Combat School" mode featured in the Neo Geo CD versions of the first two games. In 2006, Metal Slug Anthology (titled Metal Slug Complete in Japan) was released for the Wii, PlayStation 2 and PSP. This compilation includes the original Metal Slug, and all of its arcade sequels (including Metal Slug 2 and Metal Slug X) up to Metal Slug 6. The games are emulated versions of the originals, with none of the additional game modes or content introduced in the other home versions. The AES version of Metal Slug 2 was released in October 2008 for the Wii Virtual Console. Both Metal Slug 2 and Metal Slug X were also included in Metal Slug Collection PC, which was released in Europe in 2009. In 2013, versions of both games were released for iOS and Android. The original arcade version of Metal Slug X became available on Nintendo Switch via ACA Neo Geo in 2017.

In Japan, Game Machine listed Metal Slug 2 as being the third most successful arcade game of March 1998. Game Machine also listed Metal Slug X as the seventh most successful arcade game of April 1999. The PlayStation port of Metal Slug X sold 95,103 copies in Japan, and 69,035 copies in the United States, for a total of 164,138 copies sold in Japan and the United States. The later PC port of Metal Slug X sold 229,374 digital copies worldwide on Steam, for a total of at least 393,512 Metal Slug X copies sold for the PlayStation and Steam platforms.