Goblin

We found the goblins when we were trying to find our ways to the surface the first time. They attacked us and ate our dead we were forced to leave behind. Goblins are fetid, fecund, and stink something awful. They would make good allies, if it weren't for their appetite for dark elvish flesh.

Goblin society is defined by anarchy, cowardice, and malice. Goblins
are shortsighted, focused solely on the now; they're all but incapable
of planning more than a few days in advance. Unless they can find more
prosperous folk to steal from—including other goblin tribes—they live a
hard life of scrounging bugs and hunting small game to fill their hungry
 bellies. Wherever goblins travel, they leave a path of destruction and
mayhem in their wake. Adaptable to many environments, they can change
and evolve within a human's life span—a few generations for goblins—to
become better at surviving in a given environment, which makes fighting
them even more difficult the next time around.
Comfortable with living in garbage and oblivious to the concepts of
sanitation and hygiene, goblins are easy to track by scent.
Unfortunately for loot-crazed adventurers, goblins rarely have anything
worthwhile to claim; their "treasures" might be a polished tin cup, a
handful of red rocks, or a stick that intoxicates you when you chew it.
Even the chief's treasure, stolen away from other goblins and hidden
about the tribe's lair, is rarely worth more than a few gold coins.

Though goblins are as agile as rats, they're strangely
accident-prone. In battle, their attacks are often as dangerous to
themselves and their allies as to their enemies. When properly motivated
 by a powerful chieftain, an iron-fisted bandit, or a hobgoblin warlord,
 a large gang of goblins can cross the line from dangerous nuisance to
true threat, but this is more a factor of strength in numbers than skill
 or training. Smarter masters use goblins as distractions or to cause
havoc, relying on their activities to cover up a more devastating attack
 from a different direction. Settlers and adventurers who are familiar
with goblins recognize that when these pests act uncharacteristically
brave, competent, and loyal, something unusual is going on.

Goblins grow quite rapidly, and are considered adults at 5 years of
age. Abundant breeding, fast maturation, and adaptable physiology give
goblins the ability to thrive in nearly any climate. In times of
abundance, goblins multiply even faster than normal, resulting in
overpopulation and the eventual escalation of raiding. Goblin parenting
consists primarily of making sure young goblins get food and don't
wander too far. Until they're old enough to walk freely among the rest
of the tribe, goblin young are often restrained with chains, ropes, and
crude cages. Violence among young goblins is quite common and even
encouraged by their tribes. Entertainment in the form of toddler goblin
fights is not unheard of, and they may be armed with small knives,
scavenged armaments, or just their own juvenile teeth and claws.

Goblins who reach physical maturity are expected to be able to feed
themselves; those who can't are left to starve. The abilities to hunt,
to steal, and to bully weaker folk lead to positions of influence and
power within the tribe. Their species-wide illiteracy (born of a
superstition that writing steals the words out of your head) means even
the few goblins with a talent for magic or alchemy have little
opportunity to learn about these subjects. As a result, practitioners of
 these difficult arts are often both awed and feared. Some goblins have a
 special knack for crafting weapons and mechanical objects used in the
act of murder or destruction, though not many have the patience or skill
 with machines that kobolds do.