Combine mashed potatoes, butter, sugar, cinnamon, and vanilla; beat at medium speed of an electric mixer until smooth. Add crushed pineapple and raisins; stir well.
Spoon mixture into a wellgreased 3-quart casserole. Bake at 350° for 15 minutes. Top with marshmallows. Bake an additional 10 minutes or until marshmallows are golden brown.