Vehicles and weapons
Metal Slug 2 added several new weapons to the player's arsenal. A single shot from the Laser is capable of killing a column of infantry, and sustained fire can quickly destroy vehicles. Fire Bombs found in the second level can help to clear away mummies. Armor Piercing Shells give the Metal Slug tank cannon shells that only fire straight, but which do tremendous damage.
The game also included more vehicles. Though just as susceptible to enemy fire as the Metal Slug, these vehicles provide alternate modes of transportation, with each having their own advantages.
The "Camel Slug" is a Vulcan cannon mounted on a camel. The rider is elevated and still vulnerable to enemy fire, but has improved movement.
To help fight a boss that crawls up a tower, the "Slugnoid" armored frame is capable of leaping great heights. Its cannon is pointed downward, to assail the enemy attacking from below. Twin Vulcan cannons provide firepower, but they are stripped each time the Slugnoid is hit.
The "Slug Flyer" is a VTOL jet fighter which can fire powerful air-to-air missiles. It also has a Vulcan Cannon, which is designed to fire upon forward targets. Another player can "wing-walk", or ride on top of the plane.
Character transformation
Metal Slug 2 also introduced the ability for characters to transform during the course of the game. The first transformation is into a mummy during the second mission. Any hit from the purple tinged attacks of the mummy-variants or potions dropped by bats will trigger the transformation. This causes a drastic reduction in player movement speed and loss of any special weapons. Mummified characters hold only a pistol, which they fire at a rate of 50% slower than normal. Tossing a grenade also takes longer. Players also cannot use the knife, make use of heavy weaponry or vehicles when mummified. If the player is hit by another purple mist whilst mummified, they will die. Antidotes which can restore the player to human form are hidden throughout the level, dropped by enemies and given by rescued POWs.
Another transformation is the ability to become obese. This transformation is effected by eating too many food items during a single game-life. Once enough food is obtained the announcer yells "Uh-oh, big!," and the character is radically transformed. Movement speed is slowed, and every weapon's attack is altered: melee attacks are changed from a knife to a fork (or a belt whip if sitting), grenades are changed to larger cherry-style bombs, and the current weapon is replaced with a version that has larger bullets, and its offensive properties improved (for example, the rocket launcher has an improved tracking ability). The player returns to regular form if a diet-powder canister is found, enough time passes without picking up any food items, or if the player is killed.
Supporting characters
As well as doubling the number of available player characters from two to four, Metal Slug 2 is the first game in the series to introduce 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).
Plot
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 apparently killed the evil General Morden, who had staged a coup d'état against the worlds' governments. Since then, various factions sympathetic to Morden have been in operation, but have always been considered insignificant. Recently, however, they have begun to act in unison, and army intelligence concludes that the only way this could happen is if Morden himself is in fact still alive and is attempting a new coup. As such, Rossi (now a Major) and Roving (now a Captain) are sent to once again battle Morden. However, such is the importance of the mission, that 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 Mother ship. As the ship explodes (the scene reminiscent from the movie Independence Day), 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.
Reception
Upon their initial appearance, both Metal Slug 2 and Metal Slug X received generally positive reviews. Many of the subsequent ports and re-releases have received mixed reviews. For example, the iOS version of Metal Slug 2 holds an aggregate score of 77% on GameRankings, based on 5 reviews, and 76 out of 100 on Metacritic, based on 6 reviews.
When Metal Slug 2 was released on the Virtual Console in 2008, IGN's Lucas M. Thomas scored it 7.5 out of 10. He was highly critical of the slowdown (a common criticism of the game when it was first released, and one of the major selling points for Metal Slug X), but praised other aspects; "It's still a pretty solid game on its own, and there's no denying it's both hilarious and filled to the brim with great run-and-gun action." Eurogamer's Dan Whitehead scored the game 7 out of 10, criticizing the price; "The Metal Slug Anthology collates seven games from the series on disc, and can now be bought for just over twice the price of this solitary offering. If you like frantic blasting and silly humour then I heartily recommend you seek out Metal Slug. Just don't feel obliged to do it via Virtual Console."
EuroGamer's Tom Bramwell scored the 2001 PlayStation version of Metal Slug X 8 out of 10. Although he felt the game was somewhat dated by current PlayStation standards, he concluded "Metal Slug X is a fan-pleasingly simple update to the MS series, and to the rest of us it's the best game of its kind on the PlayStation." Game Revolution's Johnny Liu rated the game a B, writing "as there are fewer and fewer good Playstation games, let alone a quality port. You could do much worse these days." GameSpot's Ryan Davis scored it 8.2 out of 10, writing "What really separates Metal Slug X from the rest of the crowd is its tongue-in-cheek presentation. For example, enemy soldiers laugh when you die but shriek in horror when they realize you've come back. Or when a certain midboss is defeated, his corpse falls off the screen and is devoured by a giant killer whale. This skewed sense of humor, combined with its frenzied gameplay, gives the game a unique flavor and makes it one of the best side-scrolling shooters out there."
