Gauntlet: The Third Encounter1990

Generations ago an enchanted Star Gem crashed to Earth at the base of an ancient castle. Loathsome creatures crept from the castle and carried the Gem into the depths of the fortress.
All attempts to retrieve the Star Gem failed. The adventurers were destroyed.
The creatures in the castle gain magical strength from the Star Gem. Unless the Gem is taken from them, the evil ones will soon have the strength to venture forth and destroy mankind! You and your friends must take up the quest to rescure the Star Gem…and your world!