Introduction to Goblins
Goblin Warrior
Goblin Warriors are the backbone of the Goblin army, as they are usually the first unit that you get and they are the most easily spammed. Costing only 75 resources, they make for excellent harassers and shields for protecting more important units. Their ability to use Poison Blades, which greatly increases damage against all units and buildings, makes them unique. Watch out for the Nazgul because Goblin Warriors die in one trample.
Wildmen of Dunland
Wildmen of Dunland are a deadly addition to the Goblin army. They have the ability to set units on fire, deal splash damage, can stealth in trees, and steal resources. Versus Mordor, these units are very important. Capture the Inns and spam these units constantly.
Goblin Archer
For their price Goblin Archers carry a lot of punch. They are invaluable in this match up
for countering Orcs, pikes, Fellbeasts, and Mumakil. The Poison Arrows they can shoot are one of their most important uses. Getting one or two of these units early-game never hurts.
Spiderlings
Spiderlings as the fastest cavalry in the game and are useful in almost any match up. Sadly, their worth is not large against Mordor with the huge arsenal of cavalry counters that Mordor possesses. They can be useful for harassing though.
Spider Riders
Spider Riders have one of the best trampling abilities in the game, and they have bows. Use them to counter the huge Orc spam Mordor can throw out, and even Fellbeasts with their bows. Just watch out for pikes.
Cave Trolls
Cave Trolls are sturdy, fast, and can decimate any unit with its bare hands, or even better with a tree. They lead the front line of the battle. This siege unit has two awesome abilities that make it priceless in this match up. First, they can tear a tree straight out of the ground and gain knock back abilities for fighting Nazgul, Orcs, pikes, etc. Second, they can pick up a Goblin and take down fort expansions from afar.
Half-Troll Marauders 
The Half-Troll is debatably the most important unit against Mordor. Awesome speed and armor make them very important for harassing. They can also be used to protect Tunnels from harm. Just remember to watch out for archers.
Mountain Giant 
Towering over almost any unit in the game stands the Mountain Giant. They throw massive boulders to demolish buildings to the ground. Mountain Giants allow you to topple a fort from afar. In addition, they can stomp enemies into oblivion with a rechargeable power ability.
Gorkil the Goblin King
The king of the Goblins is not to be underestimated. With his large arsenal of abilities, Gorkil complements armies well, and with his sword, he helps counter almost anything Mordor can send at you.
Shelob
Shelob is an awesome hero, but she loses her worth against pikes and Mordor's heroes. She can be useful if he goes for lots of Corsairs and almost no pikes, but it is not likely.
Drogoth
You will not see Drogoth until late game, for he costs 5000 resources, but when you do have a chance, he is well worth the cost. Swooping to kill whole battalions and breathing fire, he devastates enemy armies. His primary use in the Goblin against Mordor matchup is to counter Fellbeasts and the Witch-king. Remember to keep him near backup at all times until he reaches at least rank six. When used correctly, this hero spells the end of the game for Mordor.
