This is played with a standard chess army (plus two extra kings) on two 8x8 boards. The regular armies are set up as normal on one board (the World), while the two extra kings are set up on the usual king positions on the second board (the Underworld). The object is the checkmate the opponent's king on the World.
Play is the same as in orthochess, except that when a piece is captured it is dropped on the nearest unoccupied square on its home file in the Underworld (pawns cannot occupy the first rank when dropped, and are dropped on the same file they are captured on). Play on the Underworld is the same as play in orthochess, with the following differences:
- Only the enemy Underworld King is capable of actually capturing pieces permanently. Otherwise captures in the Underworld are treated exactly the same as captures in the World, resulting in the piece being dropped back in the Underworld.
- There is no pawn promotion. To pawns, the board is cylindrical, with the first rank following the eighth.
- Underworld Kings have the same restrictions as regular Kings, except that "checkmating" them does not end the game, and if the Underworld King cannot escape check, its player may make any otherwise legal move. Successfully capturing an Underworld King with a regular piece results in the regular piece being returned to the World in the closest unoccupied space on its home file (the file it captured on for pawns). If the capturing piece is the other Underworld King, the capturing player gets to choose any of his pieces (including "permanently" captured ones) to return to the World, and the captured Underworld King is returned by its player to any unoccupied and unattacked space on his first rank (2nd rank if there are no qualifying spaces in the first).