Resist The Fear - Conquer the effects of the Scarecrow's fear gas
Basically all you need to do here, just as before, avoid being seen by Scarecrow for the first part. Towards the end he will spawn some skeletons for you to defeat which shouldn't be much of a problem. After fighting the normal skeletons there will be a big one which you need to throw a batarang at when it charges at you and it will break against a wall.