Collect the indicated items to get extra points. Note: They will not appear in your inventory.

Chapter 1 Bell: In the room with the three bells, slide underneath the lowest one. Jump up into it and the bell will drop down to your left.
Chapter 2 Crown: Hit the following keys on the piano (counting from the right): 5 white, 5 black, 6 white, 5 white, 2 black, 5 white, 5 black, 6 black.
Chapter 3 Moai: Wake the Boss and let him clear the room. Then, jump kick through the center of the vortex in the background and the Moai will appear there.
Chapter 4 Goemon: Find the a small dark alcove jutting out of the wall at the right side of the level. Enter it and the Goemon will appear to your left.
Chapter 5 Vic Viper: Enter the top right corner of the right building and tap Up. Vic Viper will fly across above the building from the right.
Chapter 6 Konami Man: Jump up next to the blue roof before the final staircase and tap Up. Konami Man will fly in from the right and just above you.