Place the pineapple chunks and mandarin oranges in a colander in the sink. Let them drain for at least 10 minutes to remove excess liquid.

In a large mixing bowl, combine the thawed whipped topping and the dry instant vanilla pudding mix. Stir gently until the powder is fully dissolved and the mixture is yellow and fluffy.

Add the drained pineapple and mandarin oranges to the bowl. Fold gently with a spatula to coat the fruit without breaking the mandarin segments.

Fold in the mini marshmallows until evenly distributed.

Cover the bowl with plastic wrap and refrigerate for at least 1 hour to allow the flavors to meld and the marshmallows to soften.

Stir gently before serving chilled.