Generations voyager Sandstorm's legs. On the inside of the legs there's a cavity and a tab, which serves no obvious purpose. But if you take the wings off from the mushroom peg, it fits perfectly in that leg cavity (clearly design for it to fit), with a slot to fit the tab. It looks silly though with the wheel on the inside of the leg.

Has this been discovered already? Maybe from unused design, or an easter egg transformation feature?