Step 1: Grease a 9×9 inch baking pan with butter or line with parchment paper for easy removal of your scary monster rice krispies treats.
Step 2: In a large pot over low heat, melt the 4 tablespoons of butter until completely liquid, being careful not to let it brown.
Step 3: Add the marshmallows and a pinch of salt to the pot, stirring constantly until the marshmallows are completely melted and smooth.
Step 4: Remove from heat and stir in the vanilla extract. Divide the marshmallow mixture into separate bowls if you want multiple colors for your scary monster rice krispies treats.
Step 5: Add gel food coloring to each bowl and stir until the desired vibrant monster color is achieved.
Step 6: Gently fold in the rice cereal until every piece is coated in the colored marshmallow mixture.
Step 7: Press the mixture into the prepared pan using a buttered spatula, ensuring you do not pack it too tightly.
Step 8: While the scary monster rice krispies treats are still slightly warm and sticky, press the candy eyes into the top in various patterns.
Step 9: Allow the treats to cool completely for at least 30 minutes before cutting into squares and serving.