Add the marshmallows, corn starch and coconut oil to a microwave safe bowl.
Microwave on high for 30 seconds until the marshmallows expand.
Add the food colouring drops on top of the marshmallows or coconut oil (not to the corn starch).
Stir with a spoon to combine all the ingredients.
When it gets too hard to stir, kneed it by hand until the colour and ingredients are completely combined. (Be careful, it might be hot.)
If it's too sticky, add more corn starch. If it's still too sticky, add more coconut oil. Cover your hands in coconut oil to keep it from sticking to you.
Play with it on a non stick surface, such as parchment paper taped to the table or a silicone baking mat.