Medusa is a Go game played on a base-10 hexboard with 61 'holes', so that a corner cell has 2 liberties, a cell on the edge 3, and a cell on the inside 4, as in regular Go.

On each turn a player has the following options:

1. Drop a stone on an empty cell.
2. Move one or more of his groups (a group is a set of connected stones).
3. Drop a stone and then move one or more groups.
4. Pass.

The player with more points wins. Points awarded:

1. One point for each stone.
2. One point for each surrounded cell.