Hill-troll

"Great engines crawled across the field; and in the midst was a huge ram, great as a forest-tree a hundred feet in length, swinging on mighty chains. Long had it been forging in the dark smithies of Mordor, and its hideous head, founded of black steel, was shaped in the likeness of a ravening wolf; on it spells of ruin lay. Grond they named it, in memory of the Hammer of the Underworld of old. Great beasts drew it, orcs surrounded it, and behind walked mountain-trolls to wield it."

- The Return of the King, The Siege of Gondor

Mountain Trolls are monstrous unintelligent creatures bred by Morgoth to imitate the Ents. They are about four meters high and feared for their brutal force or highly valued by evil commanders. However, they explode in a shower of stone when the sunlight hits them.

Mountain Trolls are much stronger and larger than normal trolls (And less intelligent. rendering them impossible to communicate). They also can throw stone at you from a distance and it turns into cobblestone when it hits the ground. They spawn in the Ettenmoors, Coldfells, and in Angmar. They can be hired from Angmar Orc Chieftains.

There is also a boss mob called the Mountain Troll Chieftain.

Behavior
Mountain Trolls attack enemies of Angmar on sight. Like mounted units, they have an increased distance at which enemies are spotted.

Evil players can tickle a mountain troll by right-clicking it with a feather. This will cause the troll to sneeze, throwing slimeballs out of its nose. Doing this will earn you the achievement "Blimey!"

When exposed to sunlight, Mountain trolls will run around in panic, trying to get to a shadowy place. If they can't escape the sunlight in time, they will shatter in a shower of rock particles. Standing in water also protects trolls from the sun.

Mutations
As of Public Beta 20, Mountain Trolls have a rare chance to spawn with two heads, as Mevans posted on the Facebook page. Two-headedness will result in more health and attack damage.

Loot
Mountain Trolls drop 0-2 troll bones and 0-2 slimeballs that represent the troll's snot. In addition, trolls can drop loot from any animal such as raw meat, wool, feathers and leather. This represents an animal that the troll ate.

Fun Facts
Along with Olog-hai, Mirk-trolls, spiders and Wargs they are the only non-NPC units that can be hired.