01 - Combine instant pistachio pudding mix and undrained crushed pineapple in a large mixing bowl. Stir thoroughly until pudding mix completely dissolves into pineapple juices.
02 - Fold mini marshmallows and chopped nuts (if using) into the pudding mixture until evenly distributed.
03 - Gently fold thawed whipped topping into the mixture using a rubber spatula, taking care to maintain the light and fluffy texture.
04 - Cover bowl and refrigerate for at least 1 hour to allow flavors to meld and marshmallows to soften slightly.
05 - Just before serving, top with additional whipped topping, maraschino cherries, and extra chopped nuts as desired.