Successfully complete the game to unlock the Hard difficulty.
Phantom R trips
In "Looting The Louvre", "Sneaking & Entering", or "To The Manor
Borne", while you are running and not about to hide behind a statue (for
example, at the end of "Lootivg The Louvre", there are a few seconds
when you are just running and not actually doing anything), select any
of the "statues" things on the touch screen, and Raphael should trip.