Phalanx is a side-scrolling shoot-'em-up originally developed and published by ZOOM in 1991 for Japanese-only Sharp X68000 home computers. As with most entries in the shooter genre, the story is minimal: players pilot a lone space-faring fighter craft, the eponymous A-144/R "Phalanx," in a one-man assault against a mysterious fleet of alien "bio-ships" that have attacked a human colony on planet Delia IV. Along with a unique power-up system, the game also incorporates adjustable ship speeds and a health meter for the player's ship, both of which were uncommon features among shooters at the time.
Phalanx was later ported to the Super Famicom and SNES by Kemco in 1992 for the game's first North American and European releases. The SNES version removed most of the anime-style cutscenes present in the X68000 version and featured new music. The SNES release of Phalanx in North America is notable for its unusual box art depicting an elderly banjo player and a distant spaceship streaking across the background, a scene that is never referenced in the game itself. A Game Boy Advance version was ported in 2001, and a downloadable remake of Phalanx based on the original X68000 version was published on the Japanese Wii Shop in 2009.
Phalanx is a side-scrolling space shooter in the vein of Gradius or R-Type. The game features three selectable difficulty levels by default, and a fourth expert level of difficulty called "Funny" can be accessed by entering a cheat code at the title screen. The player's "Phalanx" fighter craft has the ability to adjust between three different movement speeds, allowing for greater flexibility while evading threats. Unlike most shoot-'em-ups, the player's ship can take up to three hits in the original version of the game before losing a life, and ship health can be replenished by obtaining certain power-ups. Phalanx is also equipped with three weapon slots for upgradable primary weapon power-ups that can be swapped between on-the-fly. If the player obtains a fourth weapon power-up, the weapon in the left slot will be discarded to accommodate the new item. Primary weapon power-ups can be consumed at any time to activate a powerful special attack, and each primary weapon features its own unique special attack. A handful of secondary missile power-ups are fired alongside the ship's primary weapon and do not occupy a weapon slot.
Certain gameplay features were altered between Phalanx's releases across different platforms. Secondary missiles have a limited ammo supply in the original X68000 release, whereas all subsequent ports of the game feature unlimited missiles. In order to further reduce the difficulty of the GBA version, the player ship's health was increased to four units instead of three. The ship also features an additional weapons slot on GBA, granting players a total of four weapon slots.
- Energy Compressor (E): Fires energy blasts straight ahead that can be charged to unleash a larger, more powerful projectile. Its special attack, the Anti-Matter Detonator, damages all on-screen enemies for a short time.
- Homing Beam (H): Fires spheres of light that track enemies. The projectiles' size increases when upgraded. The High Energy Shield special attack creates a damage shield around Phalanx that also grants temporary invincibility.
- Needle Laser (L): A piercing laser that can pass through solid walls and enemies. The number of bolts increases with upgrades. This weapon also fires backwards once fully-upgraded. When activated, the Spiral Attack causes Phalanx to spin while auto-firing in all directions for several seconds.
- Reflector (R): Fires projectiles that bounce off of solid walls, making this weapon ideal for confined areas. Its fully-upgraded version also fires backwards. The Stalker Drone special attack creates an autonomous drone that seeks out and destroys enemies one at a time for several seconds.
- Homing Missiles (A): Secondary missiles that home-in on enemies.
- Penetrator Missiles (B): Secondary missiles that fire straight ahead and can pass through enemies.
- Guided Missiles (C): Secondary missiles that mimic the player's movements after being fired.
- Power Capsule (P): Upgrades the ship's primary weapon by one level and replenishes one unit of health. The ship's default primary weapon can also be upgraded.
- 1st Mission: Assault - Players begins their assault on the enemy fleet in the skies above Delia IV. After descending through the cloud cover, the fighter craft encounters a large enemy ship that attempts to swat the player with a pair of flailing arms.
- 2nd Mission: Under Water - Phalanx enters the planet's system of aqueducts, where the force of the water will slow the ship considerably. The submarine boss fires large torpedoes that explode into showers of bullets.
- 3rd Mission: Bio Cave - A series of tightly-enclosed passages make navigation tricky in this auto-scrolling stage. Destroying a large metal capsule at the end of the stage triggers the appearance of a small spherical boss that continuously tracks the player's ship while firing homing projectiles.
- 4th Mission: Deep Core - This fast-paced stage takes place in an enormous rocky cave with plenty of space to maneuver. The stage's boss has several parts: a large ship that fires energy bolts straight ahead, as well as a detachable organic section defended by a small orb that also fires projectiles. Once the organic section is sufficiently damaged, its eye will detach and attempt to crash into the player's ship until it is destroyed.
- 5th Mission: Destroyer - A unique stage that takes place both around and inside a massive alien spaceship. Players must carefully pilot Phalanx through the destroyer's narrow passages to defeat two mini-bosses. This opens the door to the stage boss, a mobile turret attached to the walls of a long metal tunnel.
- 6th Mission: Advertise Area - Giant billboards drift through an asteroid field in this neon-drenched space stage. The stage boss is a bio-ship with a single flexible arm and extendable neck.
- 7th Mission: Hyper Space - Phalanx enters a hyperspace tunnel leading straight to the alien base. A mask-like construct embedded in the wall at the stage's end serves as the boss.
- Last Mission: Charge - Inside the main base of the alien invasion force, players must penetrate the enemy's last line of defense before facing the game's final boss: a huge single-celled organism.