Wash cranberries and remove any stems or mushy pieces.
Shred cranberries in a food processor until finely shredded
Add cranberries to large mixing bowl and add in sugar. Stir together. Let the cranberries sit for 30-60 minutes unit the cranberries have released juices.
Add in crushed pineapple and stir. Gently add in Cool Whip and stir together.
Add in Mini Marshmallows and gently stir together until everything is well distributed.