Onyx (game)

Onyx is a two-player abstract strategy board game invented by Larry Back in 1995 and classed as a connection game. Black and White take turns placing stones on the points of a board built from interlocking squares and triangles, twelve points to a side, and each tries to join their own two sides with an unbroken chain of stones. Four stones of each colour are placed in advance, Black moves first, and stones do not move once placed. What sets Onyx apart from other connection games is its capture rule. If two enemy stones sit on opposite corners of a square, a third corner holds one of your own stones and the midpoint is empty, placing a stone on the last corner removes both enemy stones, and a placement that completes two such squares at once captures four. A stone may be put on the midpoint of a square only while all four of that square's corners are empty. The Ludii Portal lists the game as a modern board game in its space and connection categories.