So I have a game mechanic which needs both a goal, and probably some playtesting as well.

Play proceeds on a go board, with each player having their own color of stone. On your turn, you can either place a stone of your color, or move one of your stones already on the board to any adjacent square (including diagonals).

However, if, at the start of your turn, at least one of your stones is in the same row or column as an opponent’s stone, you must move that stone, and furthermore, the space you move it to can’t be in the same row or column as any stones it started off in line with. (So you can’t ‘threaten’ (move into line with) the stone that just threatened you, although moving it to threaten another stone is perfectly legal)

If you’ve got multiple stones threatened, you can pick which one to move.

As far as goals go, having more stones is good, so forcing your opponent to move stones instead of being able to place them is good as well (except, repeated forced moves usually allow your opponent to return the favor and force you into moves. Does it ever run into an infinite loop? Playtesting should resolve questions like that) Maybe if they are forced to move a stone, but can’t move it due to all available places being blocked by stones, they lose? Or just reaching a certain number of stones on the board?