In a large microwave-safe bowl, melt butter. Stir in marshmallows. Heat on high power for 1 minute. Stir well. Heat for another 30 seconds. Stir until smooth.

Stir in Rice Krispies cereal until fully combined.

Firmly press the Rice Krispie mixture into a rimmed half-sheet pan that has been well-greased (with butter for extra flavor!) It can also be made in a 9x13-inch baking pan for thicker monsters. Refrigerate until firm.

Place almond bark in a medium-sized microwave-safe bowl. Heat on high power for 1 minute. Stir well. Continue heating in 30-second intervals until almond bark is fully melted and smooth.

Gather up 4 bowls to use to color the almond bark. Place 1/2 tsp of oil and 2 drops of gel food coloring into each bowl. Stir to combine.

Divide almond bark equally into bowls with food coloring. Stir well, until almond bark is smooth and the color is evenly distributed.

Using a sharp knife, cut Rice Krispie Treats into 24 pieces. (If made in a 9x13-inch pan, cut into 12 pieces.)

Use a butter knife to spread colored almond bark around the top 1/3 of the Rice Krispie treat. Be sure to coat the front, back, and both sides.

Place Rice Krispie Treat on a sheet of waxed paper. Immediately add in candy eyeballs, sprinkles, or other candies as decoration for your Monster.