Empty the instant pudding mix into a large bowl. Add 1 ½ cups very cold milk and whisk briskly for about 1–2 minutes until the mixture thickens and is smooth. Check for any dry pockets and whisk them out.

Spoon the thawed whipped topping into the pudding. Use a rubber spatula to fold gently with sweeping motions from the bottom up until the color is uniform and no streaks remain.

Ensure the pineapple and mandarin oranges are drained thoroughly. Pat with paper towels if needed.

In a large bowl, combine the drained pineapple, drained mandarin oranges, halved grapes, and quartered strawberries. Toss lightly.

Pour the pudding dressing over the fruit and fold gently to coat, avoiding vigorous stirring to keep the delicate fruit intact.

Fold in mini marshmallows. If serving immediately, add sliced bananas now. If making ahead, wait to add the bananas just before serving.

Cover and refrigerate for at least 1 hour; 2–4 hours is best to let flavors meld and the dressing set.

Right before serving, give the salad a final gentle stir and fold in any bananas if you held them back. Transfer to a serving bowl and garnish as desired.