The only difference between Chess with Extended Castle and regular chess is the extended castle. When castling the king may jump three squares, but it can also jump two as usual. The rook ends up on its usual square. In Chess with Extended Castle, queenside castle will occur more often as this practically gains a tempo compared with standard chess, where the king is nearly always moved again to the knight file. Certain opening systems might benefit from the extended castle, such as the King's gambit, the Wienna Game, or the Dutch Defence. Especially, the queenside castle systems in the Sicilian would be improved.