Prepare a baking tray with baking paper or a Silpat liner. Set aside.
Add the butter to a medium sized pot and melt over a medium heat. Add the marshmallows and stir using a rubber spatula until they have melted.
Remove from the heat, add the green food colouring and combine.
Pour in the popcorn and mix until all the popcorn is coated in marshmallow.
Spray your hands with cooking spray (or use butter or oil) and take a handful of popcorn and form into a ball. Set on the prepared baking tray. Repeat with all of the popcorn.
Stick candy eyeballs onto the balls of popcorn.
Put the tray in the fridge for about 10 minutes to set the marshmallow.