fun additional rule?!
A few questions:
- Can a player's own pieces fall victim to the trapdoor intended for the opponent, if said player is foolish enough to move anything onto that particular square? This makes a difference, as one would then need to always avoid the square he/she knows to be a "secret" trapdoor, both to prevent material loss and [more importantly] to keep the opponent in the dark regarding its location.
- Do players get to decide when to "activate" a trapdoor for the first time? Suppose, for instance, the opponent moves a pawn onto the trapdoor square - if given the choice, it would probably be wise not to immediately jettison this pawn, as doing so would reveal the trapdoor's whereabouts to the opponent (at a relatively small cost).
- Once the trapdoors have each "claimed" an enemy piece, do they still remain lethal? It's a pretty important question for endgames, which would often be greatly affected even by the presence of mutually known trapdoors.