In a large mixing bowl, combine the instant pistachio pudding mix with the crushed pineapple, including its juice. Use a whisk to stir vigorously for about 2-3 minutes until the mixture is smooth and well blended.

Gently fold in the mini marshmallows into the pudding and pineapple mixture for about 1-2 minutes, ensuring they are evenly distributed.

Add the thawed Cool Whip to the bowl, folding it in gently. Mix just until everything is combined beautifully, which should take about another 1-2 minutes.

Fold in most of the chopped pistachios, reserving a handful for garnishing later, ensuring they are evenly mixed into the salad.

Cover the bowl with plastic wrap or a lid and refrigerate the fruit salad for at least 2 hours to allow flavors to meld.

Before serving, sprinkle the reserved chopped pistachios and optional maraschino cherries on top. Serve cold in a large bowl or dessert cups.