Played on a 4x5 board. Two arrangements have been proposed, and the game opens by asking which one you want to play; the choice counts as the first move and is remembered for the next game.
Each player has 4 Pawns, 2 Rooks, 1 Queen and 1 King. There is no castling, and a Pawn reaching the last rank promotes to a Rook or a Queen.
A thinner army: 1 Pawn, 1 Rook, 1 Bishop, 1 Knight and 1 King each, the Pawn standing on d2 for White and a4 for Black. Castling exists here, and a Pawn promotes to a Knight, a Bishop or a Rook - there is no Queen to promote to.
"En passant" capture: yes.
Double move for Pawns (start): yes.