There is a fourth and final cardboard box to be found on the underside of the ski hill in this skill game.
Drive down the hill and lauch off the ramp in such a way that you fly upwards at a 90 degree angle. You're aiming to land on the red crates beneath the flipper.
Once you've gotten to the lower level, drive forward and up the hill of crates and you'll see a no-entry sign. This is slightly outside of the ski jump boundaries so get some speed going up the hill. When you hit the sign, the crate it is attached to will fall back, revealing a hidden room where the box sits on a pedistal in the background. However, it's rare that you will get enough speed to move forward enough to actually see the box, making this egg extremely difficult.
The box is similar to the one found in Smoke and Mirrors, with no special design on the box.
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