Cook the pasta: Bring a large pot of salted water to a rolling boil. Add the small shell pasta and cook according to package directions until al dente, about 9-11 minutes. Drain and rinse under cold water.

Prepare the veggies: In a mixing bowl, combine the drained corn, Rotel, and green onions, and fold together gently.

Make the dressing: In a separate bowl, whisk together the mayonnaise and sour cream until smooth. Ensure no lumps remain.

Combine the mixtures: Pour the dressing over the veggie mixture, gently folding it in. Add the cheddar cheese and fold until blended.

Add the pasta: Gently fold the cooled pasta into the corn mixture, ensuring even coating without breaking the pasta.

Chill before serving: Cover the bowl and refrigerate for at least 1-2 hours or overnight to let flavors meld.