Line an 8x8 inch pan with parchment paper and set it aside.
Melt the butter in a large saucepan over medium heat.
Add the mini marshmallows and stir until fully melted and smooth.
Remove the pan from heat and stir in the green food coloring until the mixture is evenly colored.
Pour in the crispy rice cereal and stir quickly until all the cereal is coated.
Press the mixture firmly into the prepared pan using a spatula or wax paper.
While the treats are still warm, press the candy monster eyes evenly across the top.
Let the treats cool completely at room temperature before cutting into squares.