In a large mixing bowl, whip the heavy cream until soft peaks begin to form. Gradually add the powdered sugar and vanilla extract, continuing to whip until stiff peaks form (approximately 3-4 minutes with an electric mixer).
Gently fold the sour cream into the whipped cream using a rubber spatula. If using Cool Whip, fold this in as well. Use a gentle folding motion to maintain the airy texture.
Fold in the mini marshmallows, ensuring they're evenly distributed throughout the cream mixture.
Add the well-drained pineapple chunks, mandarin oranges, strawberries, and halved grapes to the cream mixture. Fold gently to combine.
Gently fold in the shredded coconut and optional chopped nuts until evenly distributed.
Transfer the mixture to a beautiful serving bowl, cover with plastic wrap, and refrigerate for at least 1 hour—though 4 hours or overnight yields the best flavor development.
Just before serving, garnish with maraschino cherry halves and a light sprinkle of additional coconut if desired.