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Copyright 2025, Phil Leduc
"Whenever you find yourself on the side of a majority, it is time to pause and reflect." - Mark Twain
Obsidio is an area influence and majority board game for two players. It is played on an n x n checkerboard, where n = 7, 9 or 11, with dark corner cells.
Target tiles are uniformly distributed with each tile having eight empty adjacent cells.
On a turn, using line of sight, a player may: place one token on a dark cell; or place two tokens on two light cells; or claim one or more target cells.
The goal is to claim a majority of the target tiles by first placing four or more tokens adjacent to the tiles.
Figure 1. Setup for a 9x9 Board with 16 target tiles
Components
Components
A 9 x 9 checkerboard with 16 uniformly distributed target tiles (marked cells).
2 sets of 51 tokens or checkers which act as influence and claim tokens.
2 sets of two pawns or stacks of two like-colored checkers to indicate each player's last move.
Concepts
Concepts
Influence Token is a token placed either diagonally or orthogonally adjacent to a target tile.
Control Token is a token placed on a target tile.
Line of Sight (LOS): A token has a line of sight to a cell or token if there exists a continuous horizontal, vertical, or diagonal line of zero or more empty cells between the token and the destination cell. Tokens and target tiles block line of sight.
Line-of-Sight Rule: When placing an influence token, if possible, the token must have a line of sight to the last placed influence or control token regardless of ownership. A series of placements can terminate because there are no empty LOS cells available, or, if a player chooses to claim one or more target tiles by placing control tokens.
Control Rule: A player may place a control token on any unclaimed target tile if that player has four or more influence tokens adjacent to the target tile cell.
Pie Rule (Swap Rule): After the first player's first move, the second player may choose to swap tokens with the first player in lieu of moving. Instead, the second player uses the first player's move as his or her own. The first player then moves again using newly aquired tokens. Thereafter, players alternate taking turns with no further swapping.
Obsidio is latin for "siege" or "blockade".
Game Play
Game Play
To start the game, the first player may perform actions 1 or 2 below. The pie rule may be applied on the second player's first turn. Player turns then alternate.
On a turn, a player may perform one of three possible actions. A player may:
Place one influence token onto an empty cell which is diagonally adjacent one or more target tiles (on dark cells). If possible, the placed token must have a line of sight (LOS) to the last placed token. Otherwise, if LOS is not possible the player may start a new chain of LOS placements. LOS is blocked by any player tokens and target tiles.
If possible, place two influence tokens onto empty cells which are orthogonally adjacent to target tiles (on light cells). Line of sight rules apply for both placements. However, if no LOS exists for the first placement, the first token can start a new LOS chain by placing the first token on any empty cell that is orthogonal to a target tile. The second token must satisfy LOS and cannot be placed adjacent the the first. If a player is unable to satisfy these two conditions, the second placement is forfeited.
Claim one or more target tiles provided four or more owned influence tokens were previously placed adjacent to each of the target tiles. Line of sight placement is not required and a player is not required to claim all available target tiles.
Figure 2. Influence Token Placements
In Figure 2, Influence Token Placements, the black tokens labeled 1, 2, and 3 would have been placed one per turn onto the dark cells, diagonal to target tiles. Note that token 1 influences only one target tile, while token 3 influences four target tiles.
Assume the teal green token 4 is the first of two tokens to be placed onto white cells, orthogonal to target tiles. This token influences two tiles (f2 and f4). The second token to be placed must have LOS to token 4 and can be placed onto any of the white cells with small teal diamonds. The cells marked with red "x"s cannot be used because the second token would be adjacent to the first (Diagonal Adjacency). The cells marked with black "x"s have no LOS to token 4 because target tiles (f4) and previously placed tokens (g3) block LOS. Notice that most of the diamond cells will influence two more additional target tiles. The two tokens would combine to influence 4 target tiles. Token 5 only influences one target tile and if it where paired with token 4, only three target tiles would be influenced.
Figure 3. Sample 7x7 Obsidio Game
In Figure 3, Sample 7x7 Obsidio Game, diamond tokens indicate the last placed token. Small dots indicate legal placements for the next move.
The Ludii General Game System, version 1.3.13, was used to generate the game play, using AI players: Ludii AI/Alpha-Beta (Black) vs. UCT (Teal) with 30 seconds analysis time per move. UCT won 5 to 2.
For those interested, the Ludii file "Obsidio Final.lud" can be downloaded from the Game Files page. Options within the .lud file, allows for several board sizes, diagonal adjacency (on/off), and six different color schemes.
Winning the Game
Winning the Game
The first to claim a majority of the board's target cells wins the game. If a tie occurs when an even number of target tiles are present, the last to claim a target tile wins.
For example, on a 7x7 board with 9 target tiles, ownership of 5 tiles wins the game. On a 9x9 board with 16 target tiles, ownership of 9 tiles wins the game outsright. Otherwise, if each player claims 8 tiles, the player that claims the last target tile wins.
Copyright (c) 2025, Phil Leduc
Copyright (c) 2025, Phil Leduc
Please note that for now these game rules may be duplicated and distributed via the web. All rights are reserved. Those that wish to program or sell this game in any form should contact the author at philleduc.pled@gmail.com for permission or a license to do so.
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