Cushion Go

Cushion Go is a soft-finite, superko-free Go variant that plays almost exactly like Go. It was invented by Luis Bolaños Mures in June 2023. Cushion Go differs from Go in the following aspects:

• If the last placement (regardless of color) and your current placement were both incursions, you must place a neutral tile under the stone you just placed. An incursion is a placement in enemy territory. An enemy territory is an empty area connected only to enemy stones.
• You cannot make a placement that would require you to place a tile on a point that already contains a tile. Placing a stone on an existing tile is allowed. Tiles are never removed, but stones on tiles can be captured as usual. (For greater flexibility, stacking up to N tiles on the same point can be allowed, but this makes almost no difference in practice.)
• Passing is not allowed, but you can return a previously taken enemy prisoner instead of placing a stone on the board. If you have no moves available on your turn, you lose. (This is the prisoner return rule from Mathematical Go. Standard Go scoring is also possible.)

Suicide is not allowed. The ko rule is used, but not the superko rule. All known Go forced cycles are impossible in this variant. Cooperative cycles are possible.

The diagram on the left shows the final position of the longest known high-level Go game as recreated under Cushion Go rules. The game lasted 417 moves. Only four tiles () were needed, and the first tile was placed on move 298.

Tile Go is the same as Cushion Go, except you must place a tile under your current placement whenever the previous placement was an incursion. This stricter rule eliminates all cycles, even cooperative ones.

Example