Drain and discard pineapple juice.
In a food processor/chopper, chop fresh cranberries. If using frozen, make sure any liquid is drained then chop.
In a large bowl, combine chopped cranberries, crush pineapple, sugar, salt, and marshmallows. Stir to combine.
Cover bowl with plastic wrap. Refrigerate 4 hours or overnight.
Whip up 8 ounces whipped cream or use premade whipped cream.
Fold whipped cream into cranberry fluff to combine.