You control a mysterious 19th-century machine named "The Eidolon" through mysterious caves. Collect and create fireballs and encounter strange creatures like 'Greps', 'Biter Birds', 'Bottlenecks', 'Rotoflies', 'Puffer Birds' , and 'Guardian Dragons'. Each type of fireball you collect has different effects. For instance Blue fireballs freeze time, and green fireballs transform one monster into another type. A guardian dragon must be defeated at the end of each level.
Eidolon is one of the progenitors of the first-person shooter genre, with full pseudo-3D panoramic graphics. This was achieved with the use of Lucasfilm Games 3D fractal technology, also used in Rescue on Fractalus! and Koronis Rift.