Dr. Thinker

 

You can throw snowballs at cousins while on the icy section of the Princedom. Press "A" to pick up a snowball, then aim and press "A" again to throw. If you hit a cousin, they will return fire.
You can also zap cousins with lightning while riding a cloud. Go to the red flowery area and look for 2 shadows on the ground near the center. Stand in one of the shadows and press "A" to float up onto one of the clouds. You can move the cloud around once you are on it and rain on any/all the cousins you see fit. If you chose the right cloud you can even strike them with lightning by pressing "A".

Psikorps

 

You can also control the KOAC during the loading screens with the left analog, and his words with the right, aswell if your running (holding X) while in princedom you can "run down" the cousins...fun during the group cousin dancing at the jukebox.

Tofu

 

If you hold down "Y" you'll start to dance and you can gather other cousins plus you can do while hold down "X".
On the present select screen you can:
1. Hold down "X" to do an animation of your cousin running and
2. Hold down "Y" to do an animation of your cousin dancing