Spellbreaker is an interactive fiction computer game written by Dave Lebling and released by Infocom in 1985, the third and final game in the "Enchanter Trilogy". Like most of Infocom's games, it was released for many of the time's popular computer platforms, such as the Commodore 64, Atari ST and Apple II. It is Infocom's eighteenth game.
Over the course of events in the trilogy's earlier games (Enchanter and Sorcerer), the player's character has progressed from a novice wizard possessing a few weak spells to the leader of the Circle of Enchanters. Now the very foundations of Magic itself seem to be failing, and the leaders of all the Guilds in the land have gathered to demand answers. In the midst of this impassioned meeting, the crowd is suddenly transformed into a group of toads and newts! Everyone present is affected except for the player and a shadowy figure who flees the hall.
In the course of investigating the mystery, the player learns new, powerful spells that must be used in novel ways. But since magic is no longer dependable, each spell has a chance of failing. The only objects that can help to shore up the effectiveness of sorcery are the Cubes of Foundation, each of which can transport the player to a different location and strengthen certain spells.
Eventually the player discovers a terrible secret: the shadowy figure responsible for all this chaos is a dark twin. Even with magic, every action has an equal and opposite reaction; and with every spell cast, the player's opposite has grown stronger. Finally, this evil being seizes the magic cubes and uses them to construct a portal which will bestow near-infinite power. The only way to defeat the doppelgänger is to sabotage the portal, an action which also leads to the destruction of all magic.