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This page is written by the game's inventor, Patrik Hedman.

Trapper Chess

Trapper chess is inspired by Arimaa, but there's a king and there are 6 trap squares. The pieces move differently and have mostly different functions from both chess and Arimaa. Only one piece may be moved each turn. The king can't occupy the squares along the rim.

The board is 13x9.

I haven't played it so I don't know if it is a viable idea.

Setup

Starting position:
Black's first rank (white's left to right) - SPPSSSPSSSPPS
Black's second rank (white's left to right) - MMMMMMMMKMMMM

White's second rank (white's left to right) - MMMMKMMMMMMMM
White's first rank (white's left to right) - SPPSSSPSSSPPS

Squares c3, c7, g3, g7, k3 and k7 are the trap squares, and they are colored blue. The four corner squares are black, and generally speaking every other square is black or white (alternating the same way as on a chess board).

Pieces

K=King     The king moves, without capturing capacities (or even influencing capacities), like an orthodox chess king. Kings can never occupy any square along the rim of the board. They can’t step onto the rim either of their own volition or by being moved there by other means.

M=Mover     The movers move one or two squares in any orthogonal or diagonal directions, and they may change direction during the move. They may move onto an occupied square if the square immediately beyond that agent in the moving direction is unoccupied. Then the occupant will be pushed to that unoccupied square. Movers may alternatively pull any agent after them, if the pulled agent was adjacent to the mover in the opposite square to the moving direction. Movers may not both push and pull agents with the same step, but they may push or pull one agent during one step of the move and push or pull another agent during the other step. It’s always optional for a mover to either push or pull, so they don’t have to even if they could during any move. Movers may also perform the kamikaze action of moving directly onto a trap square, whilst pulling any pulled agent in there along with them - but only when they use only 1 step to reach the trap square, and not when they need to take 2 steps to step onto the trap square (and the pulled agent must be located in the opposite direction of the direction of the move, as usual). The square on the other side of the trap square can even be occupied, and the mover can still pull the agent in along with itself.

S=Swapper     The swappers move, without displacement capture, like knight + alfil compounds (alfils are pieces that jump 2 squares away in any diagonal direction, and they may not change direction during a move). Swappers may switch location with any agent that they see (the ones that are on squares the swapper could have jumped to, had they been unoccupied). Alternatively, they may push or pull (but not both in the same move) agents in their line of sight by moving to the square the agent in question occuped (for pushing) or by moving in the direction exactly opposite to the agent. They push agents located in the “jump to” square another jump away in the same jumping direction, but this is only possible if the pushed agent thus ends up on either a trap square or an unoccupied square – if the swapper moves by a knight jump, then the pushed agent can jump over a trap square, but if the swapper moves with an alfil jump, then the pushed agent will be trapped on the trap square and forever removed from the board. If a pushed agent would have had to move with an alfil jump through a trap square, then the hypothetical “move to” square could still be occupied, and then the pushed agent will be removed from the board but the agent on the “move to” square will remain on the board. It’s always optional for a mover to either push or pull, so they don’t have to even if they could during any move. Swappers may also perform the kamikaze action of moving directly onto a trap square, and then any agent that occupied the square another jump of the same type away and in the same direction will be removed along with the swapper.

P=Puppeteer     The puppeteers move, without displacement capture, like an orthodox chess queen. They may also influence any agent (friend or foe), except for other puppeteers, along an unobstructed “line of sight”, and the line of sight is along diagonal or orthogonal directions. Puppeteers see through one trap square, but not through two trap squares, and they don’t see through the agent located closest along the line of sight. If a puppeteer moves any agent, then it can either be one step closer along the line of sight, or one step further away along the line of sight. For “one step further away”, the “moved to” square must be unoccupied – either a trap square or an unoccupied normal square works fine.  If a puppeteer moves another agent, then the puppeteer will remain unmoved, and only the influenced agent will have been moved. The puppeteer type action counts as a move for the player whose puppeteer it is. Puppeteers can neither push nor pull agents when they’re moving themselves. Puppeteers can not be puppeteered themselves, so they're immune to the effect of other puppeteers.

Rules

Rules:
¤ The game is played on a checkered 13x9 board. Most squares are white ones (58 of them), and less than half (53 of them, including the 4 corner squares) are black ones. The 6 trap squares are colored blue.
¤ There is no displacement type capture as in orthodox chess.
¤ There is no castling, no en passant, no checks, and no promotions.
¤ Any agent that steps onto a trap square is forever removed from the board. Agents are allowed to voluntarily step onto a trap square, and then they will also be forever removed from the board.
¤ Win is by forcing the opponent’s king onto a trap square, thus removing it from the board.
¤ Since the kings can’t take out enemies by displacement capture, the kings can occupy adjacent squares. 
¤ The trap squares can’t be passed through, at least not without consequences. Swappers can jump them without consequences when they jump like a knight, but not when jumping as an alfil. If they jump like an alfil over a trap square, then the swapper is forever removed from the board, and if the intended “jump to” square is occupied, then the agent on the “jump to” square is unaffected.
¤ White makes the first move, and then the players alternate, with one move made per turn.
¤ Neither player can move any agent back to the same square it occupied right before the opponent made his/her most recent move.


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By Patrik Hedman.
Web page created: 2014-03-29. Web page last updated: 2014-03-29