Hostile Creatures

Gnomoria is designed so that in-depth combat isn't "forced" on the player. Enemy difficulty does not scale with time by default, but with how you progress in the game; be careful not to delve "too greedily and too deep." Selecting the Peaceful difficulty during world creation will prevent any hostile monsters from spawning.

Doors will prevent enemies from passing but can be destroyed. When destroyed the door is left on the ground and can be placed back into position. Eventually door quality will reflect the door's durability; as of October 2012, it does not.

Hostile creatures in Gnomoria are differentiated into surface invaders and underground monsters.

Wild Animals
Wild animals will wander into your kingdom occasionally but are not initially hostile; they will fight however if attacked or cornered.

Animals include monitor lizards, honey badgers, and bears.

See the main article on this topic: Animals

Golems
Golems will arise out of unstocked items. It takes a few hundred of an item and about 4 days left unstocked to spawn a golem. Golems do not need light or to be underground to spawn but will do so close to Gnomes similar to underground enemies. Golems will drop a core based on the item they were composed of. A Lapis Lazuli golem will drop a Lapis Lazuli Golem Core. Golem cores can be used in the construction of automatons from your engineer after it has been researched. It is currently unknown how many different types of Golems there are, or the strenght of the Golem cores. It is however confirmed that golem cores do effect the starting hit points of your automaton and may in the future effect it's other stats.

See the main article on this topic: Golems

Invaders
Invaders are creatures that spawn on the surface at the edges of the map. The number of enemies that appear depends on your kingdom's Total Worth and your Attack Size setting during world generation. The creatures that can spawn in this way are Goblins, Mants and Ogres. By default, all military squads will attack these enemies on sight.

Goblins
Goblins spawn at the end of your first year. Their strength and numbers depend on your kingdom wealth. The higher your kingdom wealth, the more armed and armored goblins will spawn to try and overtake your kingdom.

See the main article on this topic: Goblin

Ogres
Ogres come in two varieties, single and two-headed. They come along with goblins and work on the same kingdom wealth mechanic. They do not wield weapons but their meaty size makes them tough enemies.

See the main article on this topic: Ogre

Mants
Mants are not tied to kingdom wealth, but are tied to food and drink stores. If you have a lot of food and drink lying around a mant scout may spawn on your map. If he leaves after sometime without harm, a mant invasion will trigger sending a force of mants based on your food and drink amount.

An explanation for mant invasion can be found here

See the main article on this topic: Mant

Monsters
Monsters are creatures found below the surface beginning from level -8, spawning in any dark areas. The types of monsters encountered and their strength increases the deeper the level they are encountered in. They can be prevented from spawning in an area by placing torches, although this will not prevent them from spawning at any exposed map edges. By default all military squads attack monsters on sight except Golems.

Monsters will only spawn near your gnomes (16 tiles or 2 floors away), so you don't have to light up a whole level to prevent spawns - only within 16 squares of where your gnomes usually are.

Trivia

 * Goblins, Ogres and Two-Headed Ogres come from the same kingdom per game. Names include "Crucifixionmusic" and "Pissgrowl".
 * Mants have no kingdom.
 * Mants and Skeletons are always female while Golems are genderless.