Chess Variants/Crazyhouse

Introduction
Crazyhouse is a variant that introduces the drop rule from chess's Japanese cousin shogi, allowing the player to reintroduce captured pieces as their own men. This has the effect of adding a new layer of complexity to the game.

History
It is unknown where crazyhouse came from, but as already stated the drop rule was derived from the rule used in shogi, the Japanese cousin of chess. Crazyhouse is one of the variants supported on Lichess.org.

Rules
Crazyhouse is played mostly like the standard game, with the exception of the new drop rule:

If a piece is captured in Crazyhouse, the piece reverses colour and is placed in a sectioned-off area just outside the board, on the side of the player who captured it. This piece is now said to be "in hand".

If a player wants to, then instead of making a move they may take one piece in their hand and place it on any empty square on the board. This counts as their turn. A dropped piece immediately begins affecting the game (e.g. a drop can be used to deliver check).

A pawn may not be dropped on the first or eighth ranks. If a pawn is dropped on its home rank, it may use the initial two-step move.

If a pawn that was promoted is captured, it reverts to being a pawn.

Sub-variants

 * Loop chess allows a promoted pawn to keep its new status when captured.
 * Chessgi allows a promoted pawn to keep its new status when captured and allows pawns to be dropped on the first rank (for White) or the eight rank (for Black).
 * Bughouse played with two boards, usually with four players. The captured pieces go to each one's partner.