Melt the marshmallows and butter over the stove or in the microwave in 30 second bursts. Stir well in between to prevent scorching.
Once the marshmallows are melted and well stirred, add in the pumpkin puree and pumpkin spice, and then gently stir in the rice cereal, coating completely but being careful not to crush the cereal.
Spoon the mixture into a lined or buttered baking pan, and refrigerate 2 hours or overnight.
Just before serving, mix your cream cheese glaze together. You can drizzle this onto your pumpkin spice rice krispie treats with a spoon or a piping bag if you want more precision.