> 5. Pieces of opposite colors sharing a square do not threaten one another.
This is going to be strange with kings. You could capture a piece in a square with a king and the king would require two moves to capture it, and if it was a queen the king couldn't move. Then just have to check the square for mate.
There are not all that many ways this could happen, though. I think you can only enter the square of the opposing king with a pawn. With all other pieces, you’d have to threaten the square first, which would be check. You could promote a pawn into the king and create a queen on its square.
The other way would be if the king itself moves. If the king moves onto a square with an opposing rook and a queen, and decides to capture the rook, the king is trapped until the queen moves. In this scenario, the queen must have moved there in the last turn, putting the king in check. Maybe that’s a new way to get a stalemate.
You don’t capture kings in chess, and I don’t think that changes in this variant (at least the article doesn’t suggest that). If you attack the square with the king on it, the king is in check. If there’s no legal move that puts the king out of check, that’s checkmate.
Perhaps interestingly, you can create a discovered check with two pieces on the same square, say two rooks. Like a double check in regular chess, you can’t remove the check by capturing, because you would only capture one of the rooks.
> Perhaps interestingly, you can create a discovered check with two pieces on the same square, say two rooks. Like a double check in regular chess, you can’t remove the check by capturing, because you would only capture one of the rooks.
That wouldn't work. The king would have been in check because of the first rook already, so either the king had to move away, the first rook would have been captured on the previous move, something would have been placed between the king and the rook, or it would have been checkmate.
Unless of course the two rooks would have been in place but you create the check by removing an obstacle, that would work.
This is going to be strange with kings. You could capture a piece in a square with a king and the king would require two moves to capture it, and if it was a queen the king couldn't move. Then just have to check the square for mate.