This is a Tier 3 unit, which means it "costs" 3 leadership points to lead (the maximum is 9, so the Goblin, while not the weakest, is relatively weak). It has quite a few "tags" (namely: Living, Tiny, Ranged, Melee, Humanoid), these are used in various skills. For example if a knight gives bonus ATK to all your Humanoid troops, the Goblin gets this bonus too. Another thing to note that this gobbo has both the tags Ranged and Melee, usually an unit is either this or that, but this unit is both.
The Goblin's basic attack is a simple strike, but it costs 0 AP (as all basic attack skills). It is a melee attack that triggers counterattack (if the enemy has it).
His AP gathering move is Hide, this gives him 1 AP and some ATK points, and a small amount of heal. This will be important later.
The Goblin's third move is Javelin, which also costs 0 AP. This is unusual, as 3rd skills usually cost 2-4 AP, but for the goblin it is free. He throws a poisoned javelin to a single enemy, dealing small-ish damage but also poisoning it. This is also a ranged attack so even if the enemy could retaliate, it won't.
His ultimate is Vodoo, which only costs 3 AP. It gives the Goblin a large ATK buff while also poisoning him. Remember that Poison does a current life percentage based damage and cannot actually kill the goblin. But, here is the trick. The goblin can heal himself (through the Hide skill), and all healing removes poisons!
The goblin (being an agile scout) also has a common passive skill, "Spot Weakness", which reduces the DEF of a random enemy unit at the start of combat.