Killed 5 enemies with a headshot while riding a Sky-Line.

This trophy is simple as long as you have a Sniper Rifle on you. While riding a sky-line you can either slow down or speed up using the left stick (PS3). All you have to do is slow down, aim down the sights and shot when you get the head in the target.

An easy place for this is either returning from Hall of Heroes, in front of the Bank of the Prophet and the Bull Yard. These areas are arena like layouts with great sky-lines.

Learning when to slow down and speed up can save you life while doing this as sometimes a rocket will show up or the soldiers start riding the lines and you need book it away from them.

Another good area, if you have beat the chapter, is the Command Deck. This area has many enemies, an awesome restart point, and skylines! When on the skyline slow down with the [ L Down ] button and shoot the enemies waiting on the deck in the cranium. Takes one try!