Whetticus has put a two-player tetherball game on the PICO-8, and it comes with a birthday message for Alex. (Heyhey, Happy birthday! :-))
The game supports two playable characters and lets you play solo against a CPU or with a friend. To win, you need to land a critical hit by striking the ball at the apex of its swing, or you can also combo the ball three times without repeating an attack. Controls are WASD plus G for jump and H for attack for player one, and arrow keys plus K for jump and L for attack for player two.