The Game of Nemoroth

The Game of Nemoroth, created by Ralph Betza in 2002, is the most complex playable chess variant ever created. Based on a cosmic horror theme, standard chess pieces are replaced with new pieces exhibiting side effects and complex interactions with each other. Multiple pieces can occupy a square and check is replaced with "compulsion," which can happen to any piece and to multiple pieces at the same time.

Twenty years after the original game's creation, the first ever computer implementation of Nemoroth has arrived, complete with AI opponent. The move generator and AI are written in C++ and compiled to a Web app via WASM, with a GUI written in TypeScript. There are many areas for improvement in the speed and playing strength of the AI, which is currently the crudest possible alpha-beta search with minimal optimizations.

Read the rules.

Changes and clarifications from the original game

The Go Aways always push in a fixed order, clockwise from top. This is a placeholder and will be addressed in a future version -- I've procrastinated on it mainly because it's a UI/UX nightmare.

Can a petrified Human, pushed to the furthest rank, unpetrify when it becomes a Zombie? Yes. This makes petrified Humans more interesting.

Can a Wounded Fiend approach and then flee a Ghast in the middle of its path? No. Passing over Ghast squares is against the spirit of how riders work, and inconsistent with how they interact with Basilisk or ichorous squares.

If multiple Zombies are pushed on an ichorous square, are they all dissolved? Yes. If only one Zombie were dissolved, it leads to the question of which one?

What if a square with multiple Zombies is ichorated? Same thing, they all dissolve simultaneously.

If a Wounded Fiend and a Zombie are on the same square and the Wounded Fiend leaves, depositing ichor, does the Zombie dissolve? Yes. The Zombie/ichor interaction is both active and passive.

A mobile piece other than a Zombie is compelled to move off an ichorous square. Is it a saving move to push a piece from an ichorous square to another ichorous square? No. Pushing from a multiple occupancy square to another multiple occupancy square is not a saving move, and neither is pushing a piece from a Ghast square to an equal distance to the Ghast.

If a Wounded Fiend leaves a square that already contains ichor, does the ichor stack to more than 10 moves or does it reset to 10 moves? It resets to 10 moves.

If a Zombie is pushed into an ichorous square containing both a Leaf Pile, is the Zombie dissolved or is it engulfed? Dissolved. Think of ichor as covering the entire square while the Leaf Pile occupies only part of it, so the Zombie would come in contact with ichor before the Leaf Pile.

Formal rules of compulsion

There are three ways by which a piece can experience compulsion: multiple occupancy compulsion, ichor compulsion, and Ghast compulsion.

A piece finding itself on the same square as another piece experiences multiple occupancy compulsion. (This cannot happen to Leaf Piles.) Multiple occupancy compulsion is satisfied by:

• Moving the piece (which always lands on an unoccupied square)
• If the piece has a single mobile co-occupant of the same color, moving that piece
• If all co-occupants are Zombies, pushing the piece onto an ichorous square, thus causing all the Zombies to dissolve
• Petrifying, engulfing, destroying, dissolving, or ejecting (pushing off the board) the compelled piece

A piece finding itself on an ichorous square experiences ichor compulsion. (This cannot happen to Zombies.) Ichor compulsion is satisfied by:

• Moving the piece legally
• Pushing the piece to a non-ichorous square with a Go Away's scream
• Dissolving the ichor with a pushed Zombie
• If the ichor has only one ply left, letting it evaporate by making any legal move
• Petrifying, engulfing, destroying, or ejecting the compelled piece

A piece other than a Zombie finding itself within the range of an enemy Ghast experiences Ghast compulsion. Ghast compulsion is satisfied by:

• Moving the piece legally (including promoting it if Human)
• Pushing the piece with a Go Away to increase its Euclidean distance from the Ghast
• Pushing the Ghast with a Go Away to increase its Euclidean distance from the piece
• If Human, pushing the piece with a Go Away to promote the piece to a Zombie
• Petrifying, engulfing, destroying, or ejecting the compelled piece
• Engulfing, destroying, or ejecting the enemy Ghast

The Compulsion Rule is:

If at least one of your pieces is compelled, you must make a legal move that satisfies at least one of your pieces' compulsions.

At no point can following the Compulsion Rule allow making an illegal move.

Adding new compulsions to your own pieces is legal, although only possible with a Go Away scream or by a Wounded Fiend leaving a square containing another one of your pieces.