Line a baking sheet with wax paper or a silicone baking mat and set aside for now.
In a saucepan, melt butter over medium heat. Add your marshmallows to the pan.
Stir until marshmallows are fully melted. Add green food coloring and stir until marshmallow mixture is completely tinted through.
Remove from heat and add Rice Krispies cereal. Fold in the cereal until all ingredients are well-coated and well-combined.
Pour rice cereal mixture onto your lined baking sheet. Press down with fingers (it’ll be less sticky if you wet your fingers with water or cooking spray) and flatten it out so that it’s a rectangle, about 7 in x 5 in in size.
Using your football shaped cookie cutter, cut out 6-8 football shapes. Alternatively, you can use the cookie cutter as a mold and press rice cereal treats into the cutter itself. There will be excess, you can reform, flatten, and cut out more shapes if you wish!
Insert a toothpick at the top center of each football-shaped treat with about ½ an inch of it left exposed.
Take about 2 oz. of your white fondant and set it aside. Color the rest of the white fondant with your green food coloring and knead until completely tinted.
Roll out your green fondant so that it’s about ¼ of an inch thick. Using the same cookie football shaped cookie cutter, cut out 6-8 fondant football shapes. Press one onto each cereal treat. If you need more, reroll out your fondant and cut again.
To assemble one alien, start with the ears. Roll 2 ½ inch spheres out of your green fondant. Flatten them out and point one end on each. Brush water on the back and place on either side of your alien’s head.
Take a small piece of green fondant and flatten it out to wrap around the exposed toothpick on the top of the alien’s head.
Roll a small sphere to place on the top of the toothpick.
Roll out 3 small white fondant circles, about ¼ of an inch in size each. Brush water on the back of each one to assemble on alien’s face.
Roll out 3 small black fondant circles and brush water on the back to put on the center of the white circles.
Take a small piece of black fondant and form a line to create the alien’s smile.
Add the small sphere to the top of the toothpick.
Repeat those steps for all of your treats. Serve and enjoy!