One turn, two actions
The board, the pieces, and the opening array are ordinary xiangqi. Red moves first.
After that it moves every single turn. It may not stay where it is, and it may not land on an occupied point, so each turn ends with the duck somewhere new. Anywhere new: it is not a stepping piece, and any empty point on the board is a legal placement.
The one exception is the move that captures the enemy general. That ends the game on the spot, so the duck never gets its half of the turn.
The duck blocks like a piece
Wherever xiangqi asks whether a point is occupied, the duck counts as occupied. It stops a chariot. It stands on the horse’s leg and fills the elephant’s eye. It screens for a cannon. It stands between the two generals.
That is a deliberate difference from Duck Chess, where the duck does not block a knight. A chess knight has no path to block. Xiangqi’s horse has a leg, the leg is a real point, and anything standing on it stops the horse. So the duck is stronger here than in Duck Chess: it freezes a horse from a point the horse was never going to occupy.
The cannon is where the timing bites. You place the duck at the end of your turn, which means the screen you build is the screen your opponent fires over. Duck placement is never a cannon platform for yourself.
This one was a choice, and it is the choice that most changes how the game feels. Chess has no cannon and no capture that needs a platform, so Duck Chess never had to rule on it. The duck could have been written as a blocker a cannon may not fire over, which would have made it a purely defensive piece and a much quieter game. It counts as a screen instead, exactly as any piece does, because a rule that asks whether a point is occupied should get the same answer whatever is standing there.
There is no check
No check, no checkmate, no warning. That comes straight from Duck Chess. You may move a piece that leaves your general attacked, you may place the duck and still leave it attacked, and you may move the general onto an attacked point. Neither half of the turn is tested for it. Your opponent wins by actually capturing the general, so miss the threat and you lose the game, not a tempo.
The generals may face
Xiangqi never lets the two generals sit on one file with nothing between them. Here they may, because a general may fly down that file and capture the other one. That ends the game, and it is the only time a general leaves its palace.
So the duck defends as well as blocks, and it is an uncomfortable defender: holding a file costs you the duck every single turn.
A sample game
An engine game at full strength, 8 seconds a move. Watch the duck rather than the pieces: a cannon is firing over it in 30 of the 120 plies, and near the end Red is using it to hold a file its general cannot survive without.
This game was chosen from 8 played the same way, for how much the duck does in it. 7 of the 8 finished; all 7 are in the companion study, one chapter each, with a note on how long each stayed competitive and what the duck was doing.
How games end
Capturing the enemy general wins. A player with no legal turn loses, which is xiangqi’s answer to stalemate and the reverse of Duck Chess, where a player with no move wins. Games also end by timeout, resignation, or abandonment, the same as any other game here.
Two rules draw. The third occurrence of the same position is a draw, and the duck’s point is part of the position, since where it stands changes what every piece can do. Sixty moves by each player without a capture is also a draw, which is xiangqi’s own no-progress limit. Duck Chess never defined draw rules, so this half of the ruleset had to come from the xiangqi side.
Where to next
Play it against the engine at any of eight strengths, or against a friend. The sample game above is one of seven in the companion study.