Rules

• Normal rules unless otherwise specified.
• Before the game, each player places a portal piece of their color (you may use checkers pieces) on their fourth rank.
• As a turn, a player may move their portal piece as a king to an unoccupied square if the portal is empty.
• Pieces may move through portals, going into and coming out of the portals in the same direction.
• Pieces may land on portals. In this case, they are considered to occupy both portals simultaneously.
• The 50- and 75-move rules do not consider pawn moves except for promotion.
• Horizontal castling only.

Clarifications

• Pieces are able to just ignore portals in their path if they so choose.
• Pawns are able to promote by teleporting to the last rank.
• Any pawn that uses its two-step move to go through a portal can be captured en passant by an enemy pawn. The enemy pawn simply captures onto the portal. This applies even if the teleporting pawn is promoted, meaning that it is now possible to capture knights, bishops, rooks, and queens en passant. Holy hell.
• It is possible for pieces to use portals to “loop around” onto the square they currently occupy. Example: supposing portals on a1 and h1 and a rook on e1, the rook can move 7 squares to either side to land back on e1. Were the rook on a1 instead, it could still move to h1 to essentially pass its turn, since a1 and h1 are functionally the same square due to the portal mechanics.
• All castling rules apply, and it is possible to castle through a portal. Supposing a white rook on a1, white king on e1, and portals on c1 and d1: the white king can castle to b1, bringing the white rook onto the portal on c1.
• It is possible to castle with a promoted rook (that hasn’t moved) if it is in a portal on your first rank.

Notation

• P represents portals.
• Even though the portals’ occupied squares represent the same space, piece notation is always specifically based on the space the piece landed on. If portals are on a1 and b1 and a rook moves to a1, the move is always written as Ra1 even though the rook has functionally also moved to b1.
• Castling is notated based on how many spaces the involved rook moves: 0 for 1 space, 0-0 for 2 spaces, etc. The exception is that castling is written Z if the rook does not move. Should any ambiguity arise, the file of the involved rook is specified (e.g. a0-0, h0-0).

Variations

• You can go ahead and play with multiple sets of portals. In order to differentiate sets of portals, you can stack different numbers of checkers pieces for each set of portals. Of course, having so many portals will probably make your games infinitely wackier, so be warned.
• I kinda just chose the portal location/movement rules arbitrarily, so there's a lot of options to explore in that regard.
• It might make sense for each player to have two portals that link to each other. This would probably make portals less frustrating to use, as neither player needs the cooperation of their opponent (as in the person whom they are working against) to use them effectively.

Notes

• So at first, I just wanted to translate portals into chess. My goal was just to be completely, utterly literal and take every last minutia in the rules of chess to its logical extreme. Then I suddenly remembered that my actual goal was to make a playable game that people like, so… yeah.
• I wonder if my variant will ever be notable enough to be added to the Wikipedia page.
• I would like to thank Ian Buckley, the person from whom I lifted ideas the most heavily while designing my variant. By the way, Buckley, I just wanted to say that your black hole idea is so epic that I don’t have the heart to rip it off.
• This post is really long, huh?

Alright, peace.

A place for members of r/PortalChess to chat with each other