Riddling Sphinx

Flying, Prowess
{2}{u}{u}: Monstrosity 1
When Riddling Sphinx becomes monstrous, reveal the top 5 cards of your library and separate them into two piles, face down. Target opponent chooses one of those piles. Keep the chosen pile, and put the rest into your graveyard.
Which creature has one voice and yet becomes four-footed and two-footed and three-footed?