Preheat oven to 400 degrees F. Spray a 9x13 pan with non-stick spray.
Combine crushed pretzels, sugar and melted butter in pan. Gently stir to combine and spread around pan evenly. Bake for 10 minutes and cool completely.
Pour entire can of crushed pineapple (with juice!) into a medium sized mixing bowl. Sprinkle coconut pudding mix on top and stir until completely incorporated. Fold in whipped topping. Transfer mixture to 9x13 pan, spreading on top of baked pretzels, making sure mixture reaches all of the edges. Set pan in fridge to keep cool while you mix the jello.
Combine 1 cup boiling water with box of orange jello. Stir until jello is completely dissolved. Let sit 10-15 minutes, until jello cools slightly. Pour on top of pineapple-whipped topping. Arrange mandarin orange slices so that they cover the entire surface of the salad. (They'll be set in with the jello once it cools.)
Cover salad with plastic wrap and set in fridge at least 3-4 hours, until salad is completely cooled and set. Cut squares to serve. Store leftovers in fridge.