Using a microwave or double boiler, melt the milk chocolate and coconut oil until smooth. Line a muffin pan with 12 paper liners.
Spoon 2 teaspoons of melted milk chocolate in each lined cup and spread about halfway up the sides using a knife or spoon. Once all the cups are done, pop the tray into the refrigerator to harden.
Make the peanut butter filling while the chocolate chills. Mix together the peanut butter, powdered sugar, ¾ cup of graham cracker crumbs, and pinch of salt. Once combined, the mixture might seem a tad crumbly, but should be perfectly mold-able. Using a small cookie scoop, scoop one scoop of peanut butter mixture for each cup. Roll into balls and place in the chocolate cups. Gently flatten so the peanut butter is touching the edges of the cup.
Using a spoon or piping bag, add equal amounts of marshmallow fluff on top of the peanut butter layer in each cup. Then, sprinkle the tops the marshmallow fluff using the remaining tablespoons of graham cracker crumbs. Pop the tray back into the fridge.
Remelt the rest of the remaining milk chocolate. Grab the tray from the fridge and top each cup with an equal amount of the milk chocolate. Pop the tray back into the refrigerator to let the chocolate completely harden.