With a wii remote, a second player can distract/help you in most of the single player games:
Octopus dance A second player can mess with the background by pointing and pressing the A button on the different objects. This will create sounds that could distract you while trying to follow the beat.
Donkey Kong's crash course A second player can point on the main player and hold the A button on their character. This creates a "slowing bubble" around the character that slows them down.
Takamaru's Ninja Castle A second player can help out by holding the enemies in place when they aim at enemies and press the A button. Note: It doesn't works on bosses.
F-Zero Racing A second player can destroy obstacles by aiming and pressing the A button.
Balloon trip breeze A second player can knock things out of their place by aiming them and pressing the A button.