Preheat the oven to 350 degrees Fahrenheit
Mix the cake mix with oil, water, and eggs
Bake for 15-19 minutes, and let completely cool
Add a few drops of green food coloring to the white frosting and mix
Spoon the green frosting into a piping bag fitted with a grass tip
Use the grass tip to make grass-style frosting on the cupcake. Do this by squeezing the frosting out to make long strings and pulling the tip straight up to release the grass frosting.
To make the truffula trees, cut a slice of cotton candy
Cut slits around the cotton candy to make it flow a little more around the edges
Cut the paper straws in half
Use a little frosting to glue the cotton candy to the straw - To do this, gently pull a cut piece apart and insert the frosted straw. Push the cotton candy around the straw.
Push the straw into the center of the cupcake.