Hobgoblin Chess
Designed by Simon Vertigo
Written by Jack Masters
Introduction
This game is effectively a combination of a number of other variants. Broken down, it is: Inchworm crowd-forming magnetic mutating lunar-hallway exploding-Pawn chessThe initial board setup is identical to FIDE chess. The object of the game is the same. The pieces are the same. And yet...
Inchworm
All pieces except Pawns move in two stages, extension and consolidation. During extension, half of a consolidated piece moves to a new square, capturing any enemy pieces on it. During consolidation, half of an extended piece rejoins the other half. You can leave a piece extended for as many turns as you like, and you can consolidate a piece back to its original square, except during castling. A King and Rook halfway through castling can remain in the halfway state, but they cannot go back to the way they started. If the King or Rook is moved or captured while in the process of castling, or the halves of the King or the square between them is threatened, you lose. When you capture half an extended piece, the other half disappears as well.Reference: Inchworm Chess.
Crowd-Forming
A piece may move onto and off of squares occupied by other friendly pieces. However, they may not move through them (except the Knight). Additionally, groups of pieces that are on the same square may move as a crowd. The crowd may move to any square reachable by the normal movement patterns of any of its members, or to the square containing the other half of an extended piece it contains. Only one member of the crowd needs to extend or consolidate (or none of them if the crowd contains a Pawn), though any of them can if they wish to (except Pawns). If the crowd contains any half pieces, it can move to the squares they could move to if they were whole pieces. A crowd can consist of all the pieces on a square, or only a subset. It may sometimes occur that by moving a crowd you consolidate some pieces and extend others. Crowd movement sometimes puts Pawns on the first rank. They can move forward one two or three squares, and are subject to en passant when doing so on any of the squares passed over or vacated.Reference: Crowd Chess 2.
Magnetic
When a piece (or crowd) moves (or extends, or captures (or both)), all pieces reachable by a Queen's move from the square that was moved to are subject to a magnetic force. Friendly pieces are attracted, and move to squares neighboring the moved-to square. Enemy pieces are repelled, and move away as many empty squares are available in that rank, file, or diagonal. If multiple pieces are on a square, they all get moved as a crowd. Magnetism also sometimes puts Pawns on the first rank.Reference: Magnetic Chess.
Mutation
When capturing, the capturing piece becomes the type of piece that was captured. If a crowd captures a piece, they all turn into that type of piece. If a piece captures a crowd, it can turn into any kind of piece in the crowd. If a crowd captures a crowd, all the pieces in it get to decide individually what type of piece they turn into. Consolidated pieces turn into consolidated pieces, extended pieces turn into extended pieces. Pawns turn into consolidated pieces. When turning into Pawns, both halves of an extended piece turn into individual Pawns. Consolidated pieces turn into two Pawns, both on the captured square. Pawns that turn into Pawns turn into one Pawn each. There's no non-awkward way to word that.Reference: Mutation Chess
Lunar-Hallway
To one side of the board is a strip of eight imaginary squares called the lunar hallway. These squares are considered to be connected orthogonally, diagonally, and by Knight's moves, to the squares of the hallway that neighbor them.At the beginning of the game there is no way to get to them, but on each turn before moving, a player may link an unlinked square of the hallway to a square of the same rank as it on the chessboard. The two squares now function as though they were the same square. Pieces on one are also on the other. You may not link squares containing enemy pieces.
When you move off of a linked square, you can emerge onto the board or into the hallway, but not both. When you move through a linked square starting on the board, you can end up in the hallway, and vice versa (Knights and crowds making Knight moves are not considered to move "through" any squares at all, they just move "over" them).
You can move through multiple linked squares this way on a single move. A Queen, Rook or Bishop (or crowd containing one of these) can enter the hallway from the board, go down the hallway a few squares, and emerge back onto the board heading in a completely different direction all in one move. Pawns continue to follow their normal array of funny little rules while in the in hallway. Note that the diagonally connected nature of the squares means a Pawn can capture to the square in the hallway directly ahead of itself. Pieces only in the hallway will not be affected magnetically by pieces only on the board, and vice versa. Pieces moving under magnetic influences that pass over linked squares will not transfer between the hallway and the board.
When all squares of the hallway are linked, players remove links at the beginnings of their turns instead of adding them, until the hallway is completely unlinked again. Then they go back to adding links, and so on. When unlinking an occupied square, you get to choose which side the pieces end up on. If there's more than one you can leave some of them in the hallway and some on the board.