The Eidolon Commodore 64

Discover the secrets of the Eidolon, a mysterious 19th century machine  crafted of wood and brass, powered by the forces of magic. If you can  control the energies of this ancient apparatus, an unseen world is yours  to explore. The inventor of this strange device disappeared without a  trace over a hundred years ago but his sketches and notes describe and  underground world populated by curious magical creatures and ferocious  Guardian Dragons. Create and capture fireballs of magical energies which  can transform them one into another. The powerful forces that propelled  the Eidolon and its inventor into another dimension still pulse through  its quaint frame, awaiting another daring adventurer to climb into the  pilot's chair, touch the controls, activate its power... — Cassette cover

The Eidolon was one of two games that were part of Lucasfilm Games'  second wave in December 1985. The other was Koronis Rift. Both took  advantage of the fractal technology developed for Rescue on Fractalus!,  further enhancing it. In The Eidolon, Rescue's fractal mountains were  turned upside down and became the inside of a cave.

The game was supplied on a flippy disk. One side had the Atari  version, the other side had the Commodore 64 version. Due to the  memory requirements (64kB), the Atari version would only run on an  XL/XE with 64kB or more memory.

Gameplay

The objective of The Eidolon is to successfully navigate through all  of the game's levels, defeating the dragon guardian at the end of each  level. The player navigates through each maze and collects energy orbs,  which come in four different colors (red, yellow, green and blue).  Along the way, various enemies wake up and attack the Eidolon,  attempting to absorb its energy. Each enemy is a specific color and  can only be destroyed by firing orbs of that color, or by using  special abilities. Some enemies also fire orbs at the Eidolon, which   can absorb them if set to the same color.

Green orbs, in addition to dealing damage to green enemies, also have  the power to transform other enemies into different kinds of enemies,  usually changing the enemy's color as well. Blue orbs can freeze  enemies temporarily, giving the player a momentary advantage in a  fight.

Each level contains three diamonds, each guarded by an enemy of a  specific color. After defeating each of these enemies and collecting  the diamonds, the player can proceed to the dragon that guards the  exit. There are eight levels in a game. The game is over when the  player has successfully defeated the final dragon or runs out of lives.

Source:Wikipedia