Follow these steps to create your Monster Rice Krispie Treats:

1. Prepare the Pan: Grease a 9×13 inch baking dish with butter or non-stick spray to prevent sticking.
2. Melt Butter: In a large saucepan, melt the butter over low heat.
3. Add Marshmallows: Once the butter is melted, add the mini marshmallows. Stir continuously until completely melted and smooth.
4. Mix in Vanilla: Remove from heat. Add vanilla extract and stir well.
5. Color the Mixture: Depending on your desired color for some of the treats, drop in a few drops of food coloring. Mix until you obtain the desired color.
6. Stir in Cereal: Gradually fold in the Rice Krispies cereal until evenly coated with the marshmallow mixture.
7. Transfer to Pan: Press the mixture firmly into the greased baking dish, spreading evenly with a spatula.
8. Cool Down: Allow the mixture to cool for about 30 minutes at room temperature.
9. Cut into Shapes: Once cooled, cut into squares or use cookie cutters to create fun shapes.
10. Decorate: Add edible eyes and colored sprinkles to each treat for a fun monster look.

By following these simple steps, you will have Monster Rice Krispie Treats that are wonderfully colorful and perfect for enjoyment!