For this achievement, you'll need to defeat four opponents in a game of Skystones, and acquire the Skystone the give you for beating them. You do not need to buy any stones from the merchant in the stage.
1. Beat Fangs in the House of Cards. This encounter teaches you how to play the game.
2. When Cali tells you to pull the chain, ignore her and go into The Boat House to the left instead. Defeat Woof and get his stone. This one can be missed, as you do not need to talk to him to advance the stage.
3. Beat Bandit, the prisoner, in a game.
4. Beat Dreadbeard in a game at the end of the stage.