Campaign Complete: Legendary
Campaign Complete: Legendary is an Achievement in Halo 3: ODST. It is awarded when the player has completed the game on Legendary and unlocked the Dare character for use in Firefight. It is worth 100 Gamerpoints.[1]
It is represented by the appropriate difficulty shield, except instead of two Combat knives and an Elite skull, there are two M7 SMGs and a human skull.
Sources