Everyone starts as a pawn. Pieces grow by eating their own side.
Choose
Merge table
Move a piece onto one of your own pieces to merge them; the result stands on that square. Red cells are upgrades.
Moves
Rules
Both back rows start as pawns, apart from the Kings on e1 and e8. There is no other way to get pieces.
Merging: a piece may move onto a square held by one of its own pieces, using its normal capturing move (pawns eat diagonally forward). The two pieces become one, as the merge table shows. Pawn + Pawn becomes a Bishop or a Knight, your choice.
Some merges are not upgrades: Pawn + Rook stays a Rook, a Queen that eats or is eaten stays a Queen.
The King may eat any of its own pieces and stays a King, so a King boxed in by its own pawns can step out by eating one. Nothing may eat its own King.
A merge is a normal move: it can’t leave your King in check, and it can be used to answer a check.
A pawn that reaches the far row promotes as usual. If it eats a friend on that row, it promotes first and then merges, so a Queen is always on offer.
Only pawns on the second row may move two squares. En passant is standard; it never applies to your own pawns.
Castling needs an unmoved King and an unmoved Rook on the corner. A Rook formed on its corner square by eating a piece that never moved counts as unmoved.
Checkmate and stalemate are standard. Draws: threefold repetition, the 50-move rule (pawn moves, captures and merges reset it), King against King, and King plus one Bishop or Knight against a lone King.