Each turn you place one spooky mark in two empty squares at once — it lives in both as a superposition (e.g. X₁ appears in two cells).
Spooky marks entangle the squares (the glowing threads). When they form a loop, the board collapses: a measurement forces every entangled mark into one real square. The player who didn't cause the loop chooses which way it collapses — tap one of the pulsing squares.
Get three real marks in a row to win. If one collapse completes a line for both players, whoever's line finished with the lower move number wins.