x-Chess is a series of Chess variants, all of them played on a 5x6 board, each introducing one or more fairy pieces to a different setup.
x-Chess: The First Mutant (CC BY 4.0) is the first of the x-Chess variants, in which only one piece is a mutation: the Archbishop.
It's a game designed to be quick and dynamic.
Each player has 05 Pawns, 02 Rooks, 02 Archbishops, and 01 King. There are no Queens, Bishops, or Knights.
White pieces: Pawns fill the row from A2 to E2; Rooks are placed on A1 and E1; Archbishops, B1 and D1; King goes on C1.
Black pieces: mirror the white pieces.
Rules
Archbishops move like a bishop or a knight. Although they cannot jump over other pieces when moving as a bishop, they may do so when moving as a knight. They can checkmate all by themselves.
Castling is not allowed.
Pawns cannot perform two-step moves as in regular Chess. Therefore, there is no en passant.
Pawns can be promoted only to higher pieces already captured by your opponent. If there are no higher pieces available to proceed with the promotion, pawns cannot move to the last row of the board.
The first player to checkmate their opponent wins.
—description from the designer