Spray a heatproof bowl and spatula with nonstick spray.
Weigh the mini marshmallow and chocolate and place in the microwave for 30 seconds at a time.
Stir the melted chocolate and marshmallow until combined. Make sure they are fully melted. Then add the water and mix. The mixture should be loose. Add the glycerin and corn syrup and mix again.
Sift in the cocoa powder and use the spatula to combine.
Add the powdered sugar one cup at a time. Place some shortening on both hands and knead until the powdered sugar is combined.
You may have to knead the fondant on the counter, in that case, place some powdered sugar on the counter and knead until the fondant comes together. Add more shortening to your hand as needed or to the fondant.
Roll the fondant into a ball. It needs to rest for at least an hour.
Place some shortening on a piece of plastic wrap, then add the fondant and place it into a Ziploc bag.