I did two characters for this instructable: Spider man and damsel...any number of characters can be used, of course, depending on your choice of favorites. This was really easy to do, just need to pick a rock or two, draw the characters on with marker or pencil, and paint! See my previous instructable of painting animals on rocks here:
Step 1: Seclect The Rock, Draw Figure, Paint
I've shown rock selected, reference picture, drawn figure, and painted Spiderman.
Step 2: Character #2; The Damsel
Rock selected, reference pic, priming rock, drawing figure with pencil this time.
Step 4: Steps in Painting
I have a computer monitor in my art room, so it's easy to use that as my reference soure as well (but not necessary).
Step 9: Coat With Polyurethane If Placing Rocks Outside
After all paint is dried, coat with varnish, water based, if you intend to display rocks outside. They would make surprise decorations for walkways, patios, gardens, flower beds, etc.