ICC Help: Crazyhouse
Crazyhouse (wild 23) is like two-player Bughouse. When you capture a piece, it becomes a piece of your color that you can place later. On your turn, you can either make an ordinary chess move, or place one of the pieces in your holding (e.g. "N@g5"). You can't put pawns on the first or eighth rank. Promoted pawns revert to pawns upon being captured. You can drop in check or checkmate. Crazyhouse has its own rating.
This game has also been called Chessgi and other names, according to http://www.chessvariants.com/other.dir/chessgi.html
Versions of BlitzIn prior to 2.5 don't handle examining Crazyhouse games correctly. BlitzIn 1.72 and earlier won't display your holdings at the edge of the board.