The Game of Nemoroth

https://www.chessvariants.com/other.dir/nemoroth.html https://www.chessvariants.com/other.dir/visit-to-nemoroth.html (the annotated game has an error at 4…Lg7-f6, which puts the Leaf Pile on a square seen by the Basilisk on e8 and should petrify it) https://azgoroth.itch.io/nemoroth

The Game of Nemoroth, designed by Ralph Betza in 2002, is a game about dangerous interactions. Pieces are pushed, petrified, engulfed and forced to flee. There is no royal piece, and you win when your opponent has no legal moves.

The opposing armies are called Alabaster and Obsidian. In the diagrams here, Alabaster is shown in red and Obsidian in blue; the explanations use those visible colours to make the examples easier to follow.

Each army begins with a row of Humans in front and a row of creatures on the back rank. In the back rank from left to right are: Wounded Fiend, Go Away, Leaf Pile, Ghast, Basilisk, Leaf Pile, Go Away, Wounded Fiend. The arrangement is mirrored for the other player.

The board looks colourful in our implementation because we highlight all the effects, which we will discuss in detail as we go through the rules.

The central concept in this game is compulsion. If one or more of your pieces are compelled when your turn begins, your move must respond to compulsion as described below. This restricts your available moves and can force stalemate.

Mobile pieces are pieces that a player may voluntarily move. Immobile pieces cannot be moved voluntarily (Mummies and statues). Only mobile pieces can be compelled.

There are three forms of compulsion:

1. Ichor: a piece is on ichor left by a Wounded Fiend and is compelled to leave the square.
2. Multiple occupancy: a piece shares a square with another piece and is compelled to be alone.
3. Flight: a mobile piece in the field around an enemy Ghast is compelled to move away from it. Zombies are unaffected by Ghasts.

More details are provided below alongside the piece that causes it. Compulsion may be satisfied simply my moving the piece, but section below covers more ways in which a compulsion can be satisfied.

It is not allowed to repeat a previous configuration of pieces on the board (the presence of ichor does not count in the configuration).

There are many interacting elements, so it is difficult to explain concepts in isolation. To start, here is a summary of the creatures, with more details in the following sections.

A Human moves one square straight forward, diagonally forward or sideways, and only onto an empty square. It does not capture. “Forward” is always towards the opponent's starting side. Upon reaching the last rank, a Human immediately becomes a Zombie.

A Zombie moves one square in any direction. It may voluntarily enter a square occupied by either player and destroys every piece there, including friendly pieces, statues and Mummies, with the exception of the Leaf Pile, which it may not enter at all. This can be useful because destroying one of your own compelled pieces is one way to satisfy that compulsion. The Zombie's destructive capture only happens when it moves voluntarily; if it is pushed onto other pieces or vice versa, multiple occupancy is triggered (unless the piece is a Leaf Pile, which engulfs everything).

Zombies are unaffected by Ghasts and Basilisk gaze. Upon contact with an ichorous square, the Zombie immediately vanishes with the ichor. If the Zombie voluntarily enters an otherwise legal ichorous square, its occupants are also destroyed.

The dots beneath both Humans show that either is a legal destination: the Zombie may destroy the friendly Human on the left or the enemy Human on the right. The Zombie may not move onto a Leaf Pile. The purple ichorous square is also a legal destination; if the Zombie voluntarily steps into it, the Zombie and the ichor dissolve together.

A Wounded Fiend slides any distance orthogonally through empty squares. It cannot jump over pieces, cross ichorous squares or Basilisk gaze, or approach Ghasts.

The blue Human blocks the Wounded Fiend’s rightward path: it may move to the empty square before the Human, but cannot capture it or pass through it.

Whenever it moves, its starting square and every square it crosses become ichorous; the destination is unaffected. A pushed Wounded Fiend also ichorates the square it leaves.

Most pieces may not voluntarily enter an ichorous square, but a Go Away may push a piece into it. A mobile piece on ichor is compelled to leave. This includes a Wounded Fiend that was pushed there.

Ichor lasts for five complete rounds (ten plies). On the final ply, its compulsion may be ignored because it expires right after. Voluntary entry is still forbidden except to Zombies. Depositing ichor on an already ichorous square resets its lifetime.

In Abstract Play, the ichor countdown runs from 5 to 1, each number covering a pair of turns.

A Zombie and ichor destroy one another:

• On a legal voluntary Zombie move onto ichor, the Zombie, ichor and all occupants are destroyed. No Leaf Pile may be there.
• One or more Zombies pushed onto ichor destroy themselves and the ichor; existing occupants survive. If the occupant is a Leaf Pile, ichor acts first and the Leaf Pile does not engulf the Zombies.

If a Wounded Fiend leaves ichor beneath Zombies sharing its square when stepping out from multiple occupancy, all those Zombies dissolve immediately.

A Go Away may move one square diagonally or leap exactly two squares orthogonally to an empty square.

Instead of moving, a Go Away may scream when at least one orthogonally or diagonally adjacent square is occupied. Every adjacent occupied square is pushed one square directly away from the Go Away.

The resolution order is chosen by the player. All immediate consequences are resolved before the next group is pushed. The order sometimes matters with Basilisks (explained in the Basilisk section).

In Abstract Play, select the Go Away and click on it again to scream. Click on adjacent groups in the desired order, or click the Go Away again to complete the selection alphabetically. If only one group is adjacent, it is automatically selected.

A scream pushes everything, including Mummies, statues and digesting Leaf Piles. It can push a group onto an occupied or ichorous square, or off the board. The position below gathers those cases into one example.

Reading the result from top to bottom:

• The Human on b5 was pushed off ichor to b6, satisfying that compulsion.
• The Human on c5 was pushed onto the enemy Zombie on d6. They now share the square and both are compelled; neither destroyed the other because the collision was forced.
• The Human on c3 was pushed onto the ichor at d2 and is now compelled to leave.
• The statue and Mummy on c4 were pushed together to d4 without changing.
• The digesting Leaf Pile moved from b3 to b2 and remains digesting because it was pushed rather than moving voluntarily.
• The Human on a4 was pushed off the edge and removed.

Every mobile piece sharing a square is compelled to be alone. Immobile Mummies and statues are not compelled. All occupants except for Mummies remain distinct.

This stack contains a Human, a Zombie and a sideways Mummy. The two mobile pieces are compelled.

In Abstract Play, the pulse in the player's colour shows compulsion. To move away, simply select the stack and a destination; if several piece types can make the move, choose the intended glyph from the stack panel.

A Leaf Pile moves one square in any direction. Unlike most pieces, it may voluntarily enter a square occupied by mobile pieces (friend or foe). It engulfs every piece already there and begins digesting them, and leaves behind a neutral, immobile Mummy the next time it moves voluntarily. A Leaf Pile may not voluntarily enter a square occupied by a Mummy or statue, but it may be pushed onto them.

In the first diagram, the dots beneath the friendly red Human at upper left and the enemy blue Human at upper right show that either may be voluntarily engulfed. The upside-down, darkened Human at lower left is a statue so the Leaf Pile may not voluntarily move onto it. In the second diagram, the Leaf Pile has engulfed the enemy Human and gained a yellow digestion marker. Then it steps away and leaves a Mummy, shown sideways in the third diagram. Being pushed does not leave the Mummy early.

When a Leaf Pile moves or is pushed onto occupied ground, the moving Leaf Pile engulfs every occupant. When any non-Leaf-Pile piece is pushed onto a Leaf Pile, the pushed piece is engulfed, including Zombies and immobile pieces. On ichor, pushed Zombies dissolve before engulfment. When two Leaf Piles meet, the moving one engulfs the stationary one. A Leaf Pile cannot voluntarily engulf a statue or Mummy. A Leaf Pile can therefore never be in multiple occupancy.

When a piece becomes a Mummy, it is no longer identifiable and no longer has any of the original properties. If two or more Mummies are on the same square, they merge immediately into a single Mummy because the outcome is for all intents and purposes the same.

A Ghast leaps exactly two squares diagonally in any direction to an empty square. A Ghast emits a 5×5 field around it. These squares are called Ghast squares, and are highlighted on the board in the owner's colours for clarity.

If an opponent's mobile non-Zombie piece is in one of your Ghast squares, it is compelled to move away from the Ghast. A friendly non-Zombie piece is restricted from moving into the field but is not compelled to leave it. If it begins inside that field and moves, it must move such that its Euclidean distance from the Ghast increases. Zombies are completely unaffected by Ghasts, so they may move freely into and within Ghast squares.

The red Human on b6 is friendly to the Ghast on d5, so it does not pulse and need not move. If it does move, only the dotted squares are farther from the Ghast. The friendly Wounded Fiend on e6 is similarly restricted to the dotted rays upwards and to the right. Wounded Fiends may also not travel through a Ghast field and end up on the other side. The blue Human on c4 is an enemy, so it is compelled to flee to one of the four dotted destinations.

A Leaf Pile may engulf an adjacent Ghast, but any other movement is still restricted by the Ghast's field. A Go Away's scream is not considered movement.

A Basilisk leaps one file and two ranks forward, or steps one square diagonally backward, in each case to an empty square. These four destinations are also the four squares it sees, painted green on the board. Any mobile non-Zombie piece of either colour on those squares is petrified into a statue.

Statues keep their identity and passive powers: a petrified Ghast still causes flight, a petrified Basilisk still has its gaze, and a petrified Leaf Pile still engulfs pieces pushed into it. The board shows a statue upside down and darkened.

Zombies and Mummies cannot be petrified. Petrification is usually permanent, but a petrified Human pushed to its far rank becomes a mobile Zombie.

Both Humans have become upside-down, darkened statues, even the one friendly to the Basilisk. The Zombie and Mummy on the two backward gaze squares remain unchanged.

When a Go Away screams, the order of pushing sometimes matters because the Basilisk's gaze is recalculated after every individual push. Below is a different position with a blue Go Away on d6, its Basilisk on d5 and a red Wounded Fiend on e5. The pieces finish on the same squares, but in different states.

When at least one of your mobile pieces is compelled at the start of your turn, you must respond to at least one of them. Instead of simply moving the piece away, you may also:

1. Multiple occupancy: separate the relevant occupants; remove, engulf, petrify or otherwise immobilise/destroy the compelled piece.
2. Ichor: push the piece off ichor; remove the ichor; remove or immobilise the piece; or let the ichor expire on its final ply.
3. Ghast flight: move or push the piece farther from the Ghast; move/remove the Ghast so the flight is resolved; turn a Human into a Zombie; or remove/immobilise the compelled piece.

Other compulsions may remain or arise, provided the move is otherwise legal. If no legal move meets these requirements, you lose.

In the position below, it is Blue's turn. The blue Human on c7 is compelled by the red Ghast on d5, but the only square that increases its Euclidean distance with the Ghast is b7, which is occupied by a Mummy (moving to b6 does not increase its distance). It therefore cannot flee voluntarily.

The Go Away on b8 can nevertheless resolve the compulsion by screaming. It pushes the Human southeast to d6. A forced push may move a piece towards a Ghast, and d6 lies in the red Basilisk's gaze from e7. The Human is immediately petrified, which is one way to remove the compulsion. The scream pushes the friendly Wounded Fiend on c8 into a stack, which introduces a new compulsion, but that is fine.

These preliminary observations are based on limited analysis, Betza's comments and my own play with myself so far.

You win by stalemating your opponent, and compulsion restricts the available moves so significantly that it is the main way to win the game. Putting multiple pieces in compulsion can be devastating, since compulsions are usually resolved one per turn while the opponent moves freely. Inflicting two or three compulsions at once is a big advantage.

A Ghast leaps two squares diagonally, so it is bound to one square colour, and its destination must be empty.

A Ghast in the enemy camp is close to winning: every enemy mobile non-Zombie in its 5×5 Ghast field is compelled to flee, and pieces on their own back rank have nowhere to go.

The response to an early Gd1-b3 is probably Gd8-b6 to stop the Ghast from advancing. A Ghast is itself a mobile non-Zombie piece, so it may not move into the opposing Ghast's field, and posting your Ghast opposite theirs denies them the empty squares their advance needs.

Basilisks can be strong if they turn the opponent's pieces into statues, and statues near the opponent's camp also restrict the movement of their remaining pieces, but a Basilisk's own movement options are very restricted. Betza says that a Leaf Pile is a good counter to it.

Petrifying your Humans to clear the Basilisk's path is perhaps a valid strategy to advance the Basilisk early.

The Go Away has the most tactical options and has the greatest potential to cause compulsions, but it remains to be seen if it can easily navigate to a square where it can be useful.