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Trapdoor Chess



Surely everybody has played one of the Super mario games on the Nintendo. Remember how sometimes Mario will climb on to something, and after he has been standing there a while the platform falls out from under his feet?

It wasn't easy to turn this into a rule for a game of Chess, but here it is...

Basic Premise

"Move it or lose it", as they say.

Actually, pieces are safe at the start of the game, and they continue to be safe as long as they don't move. Once a piece moves, it must continue moving or else it will fall through the floor.


Of course, what we are describing here is not just Trapdoor Chess, but the Trapdoor Chessboard. You can use this same idea in any chess variant from Billiards-Shatranj to Progressive-Shogi, and in fact you can use an Trapdoor Board for almost any board game, for example checkers or Stratego.

Trapdoor Chess is a very simple example, where the Trapdoor Board is used to play with the ordinary, everyday rules of modern western orthodox chess (FIDE Chess, as we'll call it).

Formal Rules

For the purists, here are the rules of Trapdoor Chess in "legal" form:
  • The rules of Trapdoor Chess are the same as the rules of FIDE chess, with the following exceptions:
  • The Trapdoor Chessboard is used instead of the normal one. (This is the only exception.)
  • It should be mentioned that if your king falls through a trapdoor, you lose, but if you give checkmate the game is over, and no more pieces can fall through. (These are not new rules, merely interpretations of how the standard rules apply to this situation.)
And here are the rules of the Trapdoor Chessboard:
  • The Trapdoor Chessboard is the same as the FIDE Chessboard except as follows:
  • Every square of the board has a time-delay trapdoor; when a piece moves on to a square, its clock starts ticking, and if the same piece is on the same square five moves later, the trapdoor opens up, and the piece falls through the board and is never seen again. The trapdoor timer is reset, so if another piece lands on that square, or if the original piece is captured, the new piece still has its full 5 moves to live.
  • Please notice that the timer is not running for the pieces in their original positions: as long as you don't move a piece, that piece is safe, but once a piece moves it must keep moving or die.


Notation is important, because people like to be able to write down the moves they made and think about them afterwards, and talk about them, and so on.

Notation for the Falling Through

Simply say that the trapdoor square captures itself, in parentheses after the regular move. For example: 1. e4 e5 2. Nf3 Nf6 3. Ng1 Ng8 4. Nf3 Nf6 5. Ng1 Ng8 6. Qe2 (e4:e4).

Strategy Ideas


Developing all your pieces is not a good idea. When you have too many mobile pieces, your choice of moves becomes limited by your need to move or die. On the other hand, if you have too few mobile pieces, you are underdeveloped and have too little force in play.

I would guess that the best idea would be to have three active pieces.

Castling is a bad idea, but it is good to be ready to Castle: you might need to run away!


Sacrificing a piece in order to force your opponent to move his King is probably a good idea, as a general rule.

Moving a Pawn in order to have it disappear 5 moves later and make way for a bigger piece makes sense. In particular, moving the Rook Pawns allows you to "develop" your Rooks without needing to move them!

Discovered Attacks

After the moves 1. d2-d4 d7-d5, White threatens to play 7. Qd1:Qd8+, forcing Black to move the King. (Both Pawns will disappear after the 6th move).


I think that a 5-move timer is correct for actual play; I think it is short enough that the trapdoors put tactical pressure on you, and long enough that you can still play.

For problem composers, 5 moves would be much too long. For a "mate in 2", a one-move timer might be good, for longer problems a two-move timer. (Note: for problems, assume that the pieces in the diagram are all "safe" *unless* you can prove by retroanalysis that something just moved. :-)

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