Give your little one permission to DRIBBLE and SCRIBBLE!
First, use as many crayon colors as you'd like to make large monster inspired scribbles on a piece of paper. Add drips of paint or watercolors, use a paint brush or a dropper and splatter away. We use the bathtub as a contained splatter station when the air gets chilly. Finish off your monster with googly eyes or cut circles of white paper and add your own eyeballs. Make sure you have a black crayon to draw some snarly teeth.
Check out Monsters Love Colors by Mike Austin, it contains super scribbles and splatters. A great introduction to color mixing for children age 2 and up.
What is your monster's name? What is he/she scared of? What does your monster eat?