Set the system date to any holiday such as Valentine's Day, St. Patrick's Day, Halloween, and Christmas to unlock special parts as the last object in the inventory screen:
-A Cupid unlocked on Valentine's Day flies in a straight path like a blimp, but it can pop things with its arrow.
-A Leprechaun unlocked on St. Patrick's Day dances when hit with a ball.
-A glowing Jack-O-Lantern unlocked on Halloween can be lit with a match, laser, or any similar ignition source. It can also be used to scare the cat when it gets near to it.
-A bat unlocked on Halloween will fly around when hit with a ball.
-A Santa Claus lamp unlocked on Christmas functions exactly like a lava lamp.