NEO-GEO Action Run and Gun 1999

Metal Slug X

Reviewed by Marcus Webb & Elena Castillo · Updated June 2025

SNK's 1999 enhanced version of Metal Slug 2 and the fan-favorite entry in the Neo Geo run-and-gun series — Metal Slug X rebalances Metal Slug 2's infamous slowdown, adds new weapons (Thunder Shot, Iron Lizard, Enemy Chaser), repositions enemy placements for improved flow, and delivers the definitive version of Metal Slug 2's stage content with performance that the original couldn't achieve.

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💡 Metal Slug X — Key Facts

→ Metal Slug X was developed by SNK and published by SNK
→ Released in 1999 on NEO-GEO
→ Genre: Action, Run and Gun
→ We rate it 9.3/10 — an absolute classic
→ SNK's 1999 enhanced version of Metal Slug 2 and the fan-favorite entry in the Neo Geo run-and-gun series — Metal Slug X rebalances Metal Slug 2's infamous slowdown, adds new weapons (Thunder Shot, Iron Lizard, Enemy Chaser), repositions enemy placements for improved flow, and delivers the definitive version of Metal Slug 2's stage content with performance that the original couldn't achieve.

Overview

The version that fixed the original. Six stages of the Rebel Army’s fortifications, Middle Eastern deserts, Egyptian pyramids, and Arctic operations — Metal Slug 2’s content at the speed Metal Slug 2 was supposed to run.

Metal Slug X exists because Metal Slug 2 had a problem. A serious one.

The Slowdown Problem

Metal Slug 2 pushed the Neo Geo hardware harder than the hardware could run. Dense sprite counts — the zombie transformation stage especially, with its large enemy models and heavy effects — caused the game to drop frames dramatically. Not cosmetic slowdown. Playability-affecting, input-lagging, effectively broken slowdown in certain sections.

The game was acclaimed despite this, not because of it. Players and reviewers praised what was visible through the technical limitation. Metal Slug X is what Metal Slug 2 was trying to be.

SNK rebalanced enemy placement throughout, replacing sprite-heavy configurations with alternatives that achieved similar gameplay density without the hardware bottleneck. Where MS2 had placed a dozen large enemies simultaneously, MSX achieves the same encounter feel with different enemy composition that stays within hardware limits.

The New Weapons

Four weapons the original didn’t have. Thunder Shot chains electricity between grouped enemies. Iron Lizard hugs the ground. Enemy Chaser tracks automatically. Drop Shot bounces.

These aren’t balance adjustments — they’re mechanical additions. Thunder Shot in a narrow corridor full of infantry performs entirely differently from the Shotgun’s direct-line damage. The new weapons require new strategies and reward players who learn the optimal situation for each.

The Animation

Metal Slug’s hand-drawn frame-by-frame sprites are the series’ enduring argument. Every character, enemy, and vehicle is drawn frame by frame at the density of theatrical animation rather than the economy of video game sprite reduction.

An enemy hit in a specific location reacts differently than one hit in another. A vehicle destroyed at full health explodes differently than one reduced gradually. POW hostages rescued after prolonged capture react with different animations than immediately rescued ones. The animation density is what Metal Slug players cite when asked why the game still looks better to them than polygon alternatives — not because it’s more realistic, but because it’s more alive.

MSX is the clearest demonstration of that animation quality, running at the speed the artists intended.

Our Review

9.3

Outstanding / 10

🎮

Gameplay

★★★★★

🎨

Graphics

★★★★★

🎵

Audio

★★★★★

🔄

Replay

★★★★★

Gameplay

Metal Slug X is a side-scrolling run-and-gun for one or two players. Marco and Tarma (plus Eri and Fio in later ports) run through six stages of the Rebel Army, collecting weapon upgrades and rescuing POW hostages. New weapons over Metal Slug 2: Thunder Shot (electric arc), Iron Lizard (ground-hugging rocket), Enemy Chaser (homing attack), and Drop Shot (bouncing grenade). New vehicles including the Camel Slug and Ostrich Slug. The game's defining characteristic versus Metal Slug 2 is performance — MS2's heavy sprite density caused severe slowdown on Neo Geo hardware; MSX rebalances enemy placement and enemy types to eliminate slowdown while adding new content. Two-player simultaneous co-op throughout.

Graphics

Metal Slug X's sprite work represents the Neo Geo hardware at its animation peak — hand-drawn frame-by-frame animation at a density and humor that no contemporary 2D action game matched. Enemy death animations, vehicle destruction sequences, and POW rescue animations are the series' visual signature.

Audio

Metal Slug X's soundtrack continues the series' blend of military marches and rock compositions. Stage music reflects the game's international settings — Middle East, jungle, Egypt — with appropriate musical references. The sound design for weapons and vehicle destruction is viscerally satisfying.

Replayability

Six stages with score optimization, POW rescue tracking, new weapon experimentation, two-player co-op chaos, and the score-attack culture the game inspired create enormous replay depth for action game enthusiasts.

Historical Significance

Metal Slug X (1999) is widely considered the best Metal Slug game or one of the top two (alongside Metal Slug 3). Its significance is corrective: Metal Slug 2 was an acclaimed sequel hampered by hardware slowdown that made certain sections unplayable at full speed. Metal Slug X is Metal Slug 2's content without its technical limitation — a 'definitive version' that replaced the original in competitive and archival contexts. The game also added enough new content (weapons, vehicles, enemy placements) to stand as a separate game rather than a patch. Metal Slug X has maintained its reputation as the series peak since 1999 in the fighting game and run-and-gun enthusiast community.

✅ Pros

+ Metal Slug 2's content without the crippling slowdown
+ New weapons (Thunder Shot, Iron Lizard, Enemy Chaser) not in MS2
+ Hand-drawn frame-by-frame animation — Neo Geo at its visual peak
+ Two-player simultaneous co-op throughout
+ Fan consensus peak of the classic Metal Slug series

❌ Cons

- Six stages — shorter than Metal Slug 3's longer structure
- Requires knowing Metal Slug 2 context to fully appreciate MSX's improvements
- Neo Geo hardware pricing for authentic play
- Egyptian pyramid stage difficulty spike can frustrate

Also Known As

Metal Slug X Neo GeoMSXメタルスラッグX

Metal Slug X FAQ

What is the difference between Metal Slug 2 and Metal Slug X?

Metal Slug X is an enhanced revision of Metal Slug 2 that addresses the original's primary technical problem while adding new content. Metal Slug 2 (1998) suffered from severe slowdown — the Neo Geo MVS hardware was pushed beyond its sprite capacity by MS2's dense enemy placement and effects, causing frames to drop dramatically in certain stages. The Zombie transformation stage and heavy-enemy areas slowed to unplayable speeds. Metal Slug X (1999) rebalances enemy placement throughout the game to eliminate these slowdown triggers, replacing sprite-heavy areas with differently structured encounters. Beyond the performance fix, MSX adds new weapons unavailable in MS2: Thunder Shot (electric arc attack), Iron Lizard (ground-level homing rocket), Enemy Chaser (targeted homing shot), and Drop Shot (bouncing explosive). New vehicle types and repositioned enemy placements further differentiate MSX as a distinct game rather than a direct patch.

What are the new weapons in Metal Slug X?

Metal Slug X introduced four new weapons beyond the classic Metal Slug 2 arsenal. Thunder Shot fires an electric arc that chains between nearby enemies — effective against grouped infantry. Iron Lizard is a ground-hugging missile that travels horizontally at ground level, useful for clearing low targets without needing precise aim. Enemy Chaser fires a homing shot that tracks the nearest enemy — the most forgiving weapon for less precise players but with limited range. Drop Shot fires a projectile that bounces off the ground on contact, useful for hitting enemies behind cover or below platforms. These four weapons expand the Metal Slug X loadout significantly beyond the original's Shotgun, Rocket Launcher, Flame Shot, Laser Gun, and Heavy Machine Gun options, requiring players to learn new use cases and optimal situations.

Why is Metal Slug X considered the best Metal Slug game?

Metal Slug X's reputation as the series peak (alongside Metal Slug 3) rests on several factors. Its performance fix made the Metal Slug 2 content actually playable at the intended speed — something the original couldn't deliver. The new weapons add variety without disrupting the core run-and-gun balance. The stage variety — Middle Eastern deserts, juntas, pyramids, high seas, the Arctic — is consistently different from stage to stage. The difficulty curve is considered well-calibrated relative to the original Metal Slug's length and Metal Slug 3's extreme final stages. The two-player co-op creates memorable chaos through the dense enemy sequences. Metal Slug X also benefits from the series being at its creative height before later entries (4 and 5) were considered lesser. The game represents SNK's hand-drawn sprite technique at maximum refinement — the animation quality has been cited as the most technically impressive 2D sprite work on any hardware.

Is Metal Slug X available on modern platforms?

Metal Slug X is available through multiple modern routes. SNK's NeoGeo libraries on Nintendo Switch Online, PlayStation 4, and Xbox platforms have included Metal Slug titles. Metal Slug X appears in the Humble Bundle Metal Slug 30th Anniversary collection and SNK 40th Anniversary Collection. The game is available on Steam. SNK's NeoGeo platform releases metal slug games regularly on digital storefronts. The ACA NeoGeo (Arcade Archives NeoGeo) series by Hamster Corporation brings Metal Slug X to Nintendo Switch, PS4, and Xbox One with online leaderboards. Physical Neo Geo AES cartridges are expensive collector's items. The Metal Slug Anthology (Wii, PSP) included MSX alongside MS1-6. Modern availability is excellent compared to many Neo Geo titles.