Goblins.
As far as people know, goblins had originally survived and lived in caves and caverns close to the surface. Eventually, they emigrated deeper into the Beneath, making homes in dungeons and other subterranean constructions. While some people believe that goblins are intelligent and cultured creatures, most believe they are primitive and vicious-natured. Generally everyone agrees that goblins aren't fun to hang around--even other goblins. Each clan is controlled by a separate monarch, known as the Goblin King. These clans have been known to interact with Imperial officials, and while they are not directly connected to the Empire, they have been bullied and manipulated to work for the Empire as guards or spies in belief that it was to benefit themselves. Although some abovegrounders have claimed to make contact with goblins, contact is so rare that it is considered to be nonexistant. Some goblins have the ability to create wooden ornaments, which they will then sell and use the money to further better their clan.
Detailed Behaviour Analysis
Goblins calculate distance to the player using the Pythagorean Theorem. They assign a score to each of the eight adjacent squares that it can enter and to its current position. The highest score (50,000 actually) goes to a square that contains the player and the lowest to any other square that is adjacent to the sword (5000).
Any other squares are assigned score in terms of their distance from the player; closer squares get higher numbers (according to the formula 5000-100*Distance) and the goblin picks the highest score of the nine possibilities. If best scores are tied, it uses the preference order: NW, N, NE, W, its own square, E, SW, S, SE. This system allows the goblin avoid the sword and also to increase their vertical or horizontal distance from the player in order to move to a diagonal tile that is closer to them, by Pythagoras' theorem - behaviour that is distinct from un-brained roach-like creatures.
Behaviour when brained
Brained goblins move the same way unbrained goblins do, except that they calculate distance differently. If there is no visible path to the player or the square is within two squares from the player (according to the brain), then distance is calculated as normal. Otherwise, distance is calculated in terms of
brained distance, with a preference towards nondiagonal moves.