1. First, melt vegan the butter in a large stock pot. Once the butter is melted, add the vegan marshmallows and green food coloring. Stir continuously until the marshmallows have mostly melted and the food coloring is evenly distributed.
2. Once the marshmallows have melted, remove from heat. Stir the vanilla extract and rice cereal into the melted marshmallow. Mix until all of the cereal is evenly coated with the marshmallow mixture.
3. Transfer the mixture to a lightly-oiled 9×13 baking dish. It is super helpful if you have a baking dish with a lid to make for easy storage. Let the mixture sit for 20 minutes before slicing.

For the Frankenstein Design

1. Once the treats have cooled and firmed, slice them into 16 even sections. Remove the sections and place them on parchment paper or silpat.
2. Use an icing spatula to spread the black icing over the top 1/4 of the treat in a rectangular and slightly uneven pattern. This is the monster's hair.
3. Use the fine-tipped decorator icing to make the mouth and two small dots to help the candy eyes adhere.
4. You can make these happy Frankenstein monsters or grumpy or whatever you please! Enjoy!