From the Super Mario Wiki
Rhythm Hammer is a souvenir in WarioWare: Twisted! in the Instruments folder. It features a white hammer with a simple face on its head. The hammer can be moved by tilting the console, which rotates it towards the shapes on either side of the screen. On the left is a circle, and on the right is a diamond, which make a different sound when hit with the hammer. By pressing , the shapes change color and produce a different sound: white creates drums, yellow creates cymbals, beige creates miscellaneous percussion sounds, green creates bongos, grey creates steelpans, cyan creates typical WarioWare sound effects, red creates car horns, and pink also creates typical WarioWare sound effects. The colors cycle around in the previous order.