Add apple to a large bowl and toss in lemon juice to keep from browning.
Add the pineapple, mandarin oranges, grapes, coconut, and marshmallows and toss to combine.
Stir in Greek yogurt, gently tossing to coat.
Refrigerate for at least 4 hours prior to serving to allow the flavors to meld together. Serve chilled.
Notes
After a day or so of sitting in the fridge, liquid from the fruit may pool at the bottom. If eating the leftovers, I like to gently pour some of this off before eating.