The Eidolon is an innovative first-person shooter developed by Lucasfilm Games in 1985, utilizing advanced fractal technology to create immersive cave environments. Players navigate through eight levels of maze-like caverns, collecting colored energy orbs and battling various enemies. The game's unique combat system requires matching orb colors to enemy types, adding a strategic layer to the shooting mechanics. Each level culminates in a battle with a dragon guardian, accessed after collecting three diamonds guarded by specific enemies. The game features special abilities tied to orb colors: green orbs can transform enemies, while blue orbs temporarily freeze them. This color-based gameplay, combined with the need to manage the Eidolon's energy levels and navigate increasingly complex cave systems, creates a challenging and engaging experience. The Eidolon's blend of cutting-edge graphics technology, strategic combat, and exploration elements made it a standout title in early 3D gaming, showcasing Lucasfilm Games' innovative approach to game design in the mid-1980s.

The player discovers the Eidolon, a strange 19th-century vehicle in an abandoned laboratory. As the player investigates this device, he is accidentally transported to another dimension and is trapped in a vast, maze-like cave. The creatures in this cave, sensing the energy emanating from the Eidolon, are awakened from a long slumber, and the player soon finds that his only chance of survival lies in this mysterious vehicle and its powerful energy weapon.