Chill your tools: Pop a large mixing bowl and a rubber spatula into the fridge for 10 minutes.
Cold tools help the salad stay fluffy.
Mix the base: In the chilled bowl, whisk the sweetened condensed milk, instant pudding mix, sour cream (or Greek yogurt), vanilla extract, and a pinch of salt until smooth and slightly thick.
Fold in the whipped topping: Add the whipped topping and gently fold until the mixture is uniform and creamy. Don’t overmix—you want to keep the fluffiness.
Drain the oranges well: Press mandarin oranges lightly with paper towels to remove excess moisture. This helps prevent watery salad later.
Add the mix-ins: Gently fold in the mandarin oranges, mini marshmallows, and coconut and nuts if using.
Mix just until everything is evenly distributed.
Chill to set: Cover and refrigerate for at least 2 hours, or up to overnight. The flavors meld and the texture firms up slightly.
Stir and serve: Give the salad a quick, gentle stir before serving. Spoon into a serving bowl or individual cups and garnish with extra oranges or a sprinkle of coconut if you like.