Animated doodling that makes your doodles pulse and spin and fade. Change colours and shades, shapes and animations. Use multiple colours at the same time.
Use multiple fingers at the same time to produce synchronized strokes.
Change the speed at which you drag your finger to create different effects.
Take snapshots of your doodle that saves to your picture library.
Undo your previous strokes/animations if you don't like them. Or just clear the canvas and start afresh.