Gameplay
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.
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.
Iridion 3D features five types of weapons, with three levels of power each. Players boost weapon power by collecting powerups of the color that matches the current weapon. 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. Each weapon has advantages and disadvantages. The player starts with the red weapon, which is relatively weak but fires rapidly in a large spread. Green weapons are inaccurate but fill the screen with shots. Purple weapons spin in a counterclockwise motion slowly and are fairly strong. Yellow torpedo-like weapons are very powerful but powerups are rare and the weapon fires slowly. Blue weapons, a more powerful version of Yellow weapons, are found only on the last level. Flashing powerups restore the craft's shields.
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