In a large mixing bowl, beat the vanilla instant pudding, pumpkin pie spice, and milk for 3 minutes. In a separate bowl, beat the cream cheese until fluffy, about 3 minutes.
Add the pumpkin puree, scraping down as needed, and continue beating until combined. Combine the pudding mixture with the cream cheese mixture until blended.
Fold in the whipped topping. Fold in the marshmallows and nuts. Serve topped with additional pecans and/or garnishes.