The forces of Morgul Vale have made their way to South Ithilien and Osgiliath, including Shardrágh, a great siege-beast from Minas Morgul.
'Let me share with you information on Shardrágh. He is a massive Morgul-troll, as strong as the great beasts that pull the Morgul seige equipment to war. Shardrágh has been seen wandering South Ithilien then returning to Osgiliath. I am not certain to what this creature's mission is - perhaps he just awaits orders for the Morgul-host to continue its western assault. Something must be done about Shardrágh before he is able use his strength in battle over the days to come.'
Shardrágh can be found somewhere in South Ithilien or Osgiliath.
You should defeat Shardrágh.