Line an 8×8-inch baking pan with parchment paper and lightly coat it with nonstick cooking spray.
Melt the butter in a large pot over low heat.
Measure out 1 cup of marshmallows from the 10-ounce bag and set them aside. Add the remaining marshmallows to the melted butter and stir over low heat until just melted and smooth.
Remove the pot from the heat and stir in the vanilla extract and salt.
Add the Rice Krispies and Count Chocula cereal. Gently fold everything together until the cereal is evenly coated with the marshmallow mixture.
Add the reserved 1 cup of marshmallows along with the additional 1 cup of mini marshmallows. Gently fold them in, leaving some of the marshmallows partially intact to create gooey pockets throughout the treats.
Transfer the mixture to the prepared pan. Gently press it into an even layer without packing it down too firmly. Sprinkle Halloween sprinkles over the top and lightly press them into the treats so they stick.
Let the treats set for 30–45 minutes. Lift them out of the pan using the parchment paper and cut into rectangles.
Melt the Ghirardelli Dark Chocolate Melting Wafers according to the package directions. Drizzle the melted chocolate over the top of each Rice Krispies treat.
While the chocolate is still wet, add a Halloween icing decoration to each treat. Let the chocolate set completely.
Place each finished Count Chocula Rice Krispies treat into a cauldron-shaped favor bag and seal. They’re ready to hand out as Halloween party favors.