Fairy chess

Fairy chess extends composition beyond the usual rules of chess. A work may introduce pieces with new movement powers, a condition that changes how moves operate, a different board, or another explicitly defined modification.

For the solver, the essential point is that the modification must be known before solving. You cannot assume that every piece, capture, or mating condition works as it does in an ordinary game. Once the special rule is stated, the problem is solved by applying it consistently together with whatever orthodox rules remain in force.

Classification boundaries can vary. The Codex of the World Federation for Chess Composition (WFCC), the international organization for chess composition, separates the type of task from the rule set used. Thus forms such as a helpmate, where both sides cooperate to mate Black, and a selfmate, where White forces Black to mate the white king, can be classified by their objective without that alone requiring a fairy piece or condition. There are also problems that reconstruct legal history and games that reconstruct a route from the initial position using fairy conditions.