Iridion 3D is a quasi-3D rail shooter video game developed by Shin'en Multimedia. A launch title for the Game Boy Advance portable game console, it was released in North America on June 11, 2001 and in Europe on September 21. The player controls a single starship defending Earth from the alien Iridion. The game spans seven levels from Earth to the aliens' home planet, each following a linear path that culminate with a boss.
Iridion began development as a shooter for the Game Boy Color; when Shin'en decided to drop development and shift their focus to the Game Boy Advance, Iridion was the first game by the developer to appear on the system. Though billed as a 3D game, Shin'en used realtime encoding and resizing to manipulate the size of 2D sprites instead of creating a true 3D environment. More room on the game cartridge was available for graphics due to the game's use of the GAX Sound Engine, which allowed real-time decoding of song data in a small file size.
On release Iridion garnered generally mixed reviews. The graphics and sound were generally praised; a year after its release, critics at Extended Play still considered it the best-looking game on the platform. In contrast, critics derided the game's repetitive and frustrating gameplay. Despite lukewarm reception to the title upon release, Iridion 3D was a financial success, and influenced future Shin'en shooters such as Iridion II and Nanostray.
The game is a simple forward-scrolling rail shooter, similar to the Star Fox series. Only the Game Boy Advance's directional pad, A, and Start buttons are used during gameplay. The ship remains locked at a set speed and cannot brake or speed up.
The player encounters more than fifteen types of enemy, not including level bosses. Some are easy to destroy; others, including the fire creatures found on the Iridion home world, are indestructible and must be avoided. Other enemies prevent the player from dodging enemy fire by laying mines to block paths. Passive objects, such as garbage or asteroids, can damage or destroy the player's craft. Enemies vary in armor and weaponry—some cannot return fire but travel in waves to ram the player. The player's ship can use five types of weapons, with three levels of power each. Players boost weapon power by collecting powerups that match the current weapon's power; collecting a different color gives the player the first level of that weapon type. If the player's ship is destroyed the power level of the weapon is reduced by one. Flashing powerups restore the craft's shields.
Each level has the player follow a linear path through waves of enemies and culminates with a boss. In boss stages the player's craft does not move forward, but hovers in front of the boss. Each boss has a single vulnerability which flashes when hit. These areas are often heavily shielded and must be hit repeatedly to remove armor. Other bosses' vulnerabilities are hidden and appear for only short periods. Most bosses have weapons that fire upon the player or reflect the player's shots. At the end of each level, players receive bonuses for defeated enemies, lives remaining, and the energy level of the player's craft. An extra life is granted if the score reaches certain thresholds.
