An action shooter game featuring a giant robot which can transform into a jet. Trapped within a mysterious facility, the goal is to navigate 16 maze-like levels and stay alive long enough to destroy the central computer.
Each level is a massive side-scrolling map filled with obstacles, enemies, and various maze-like twists and turns. Play always begins on the far left side of the map and ends on the far right. The goal is simple: get from the beginning to the end whilst still having energy.
The Thexder Assault Vehicle can transform between two modes at any time: robot and jet. In robot mode, it can fire heat-seeking lasers to destroy enemies and obstacles. Although it has the ability to jump, Thexder's robot form is generally less mobile than its jet counterpart and therefore can't access certain areas of the level. In fighter jet mode, lasers can only be fired in a straight line, making the vehicle much less useful in combat. However, the jet's increased mobility allows it to reach areas that are higher and/or smaller than the robot's larger size would otherwise allow. To be successful, players need to master the balance between these two vehicle modes.
In addition to its offensive capabilities, Thexder is also equipped with an energy shield. At any time, players can choose to engage the shield by sacrificing a percentage of their current energy level. The shield provides invulnerability, but decreases with time and with each hit taken from an enemy. Completing a level without using the shield awards a sizable bonus to the "ENMAX" (the total possible energy points that are available to Thexder). Since later levels become much more difficult, it is important to have as much ENMAX as possible. Because of this, strategic use of the shield is essential for success.