The Invulnerable Achievement / Trophy (depending on your console) in Scott Pilgrim vs. The World: The Game requires you to play through a whole level and reach the boss without taking any damage. This might seem like a challenge, but there's a very easy trick to doing it. This video will show you just that.
From the Creator:
PS3 = Square, Square, Square, X, Circle, X, Triangle
360 = X, X, X, A, B, A, Y