Place Jell-O in large mixing bowl. Add cream cheese to the Jell-O. (For easier mixing allow the cream cheese to soften before adding in.) Mix mixture until smooth and completely blended.
Drain juice from the pineapple. Add pineapple to the mixture. Mix pineapple in well. Add Cool Whip in by hand beating. (It is best to also allow the Cool Whip to soften) Add marshmallows (I use a half of a bag, you can use as many or as little as you like)
Place in bowl, and allow to set up in refrigerator for about 6 hours. Do not cover the bowl until the Jell-O fluff is set up.