In a large saucepan, combine the orange gelatin and vanilla pudding mix. Pour in hot water and stir continuously over medium heat until the mixture turns a clear orange color.

Once the mixture is clear and well combined, remove from heat and pour into a large bowl. Cool slightly, cover, and refrigerate for at least 4 hours.

After chilling, gently break up the gelatin mixture with a potato masher and fold in the Cool Whip until well combined.

Add the drained mandarin oranges and gently fold them into the mixture without overmixing.

Transfer back to the refrigerator and chill for an additional 30 minutes to 1 hour before serving.