Prepare a baking sheet with parchment paper. Set aside.
In a large pot, melt your butter and marshmallows on medium heat stirring every 20 seconds.
Once the mixture is smooth, turn off the heat.
Add a few drops of green food coloring and mix. Keep adding food coloring until you get the desired color.
Stir in rice cereal. Mix until fully coated.
Pour mixture onto prepared parchment paper.
Coat hands with water or cooking spray.
Form a cactus shape.
Set the rice krispy cake in the fridge for at least 30 minutes to cool.
While the rice krispy cake is in the fridge, use the green food coloring to dye your canned frosting.
Take the rice krispy cake out of the fridge. Carefully remove from the parchment paper and flip it over (so the smooth side is facing up).
Cover the rice krispy cake in frosting.
Starting at the top of the cactus, drag your knife down the length of the cactus to make a groove. Repeat all over the cactus.
Add your sprinkle spikes.