Stir together the cheese spread and pineapple in a large bowl. Add the marshmallows, stirring well to combine. Fold in the whipped topping and mix well. Serve immediately or cover and refrigerate overnight.
The key to this is mixing, mixing, mixing. Mix until you think it's mixed, and then mix it some more! You will see it getting fluffier and more cohesive. I find it's best if made the night before and refrigerated.