Cut your large marshmallows in fourths. I use scissors to do this. You may have to dip them in hot water from time to time when they get sticky.
Cut your red grapes in half if they are small ones or fourths if they are large ones.
Drain your large can of crushed pineapple VERY VERY well. You don't want any liquid in the salad. I dump it in a colander and then us the lid to press down on the pineapple to help with the draining process.
Combine first 3 ingredients and then fold in Cool Whip. Make sure everything is well incorporated. Allow to chill in refrigerator before serving. Enjoy!