Hi! Here is my cute Monkey D. Luffy as a keychain and a magnet.
The design is made so you can print it multicolour even if you don´t have multifilament printer. Each layer/colour has slightly different height so in your slicer you can set automatic change of colour. You print one layer, pause the print, change a filament and print another colour etc. 
Recommended size is 60mm
Recommended height is 4.5mm