Dog

The guard dog can be found in the first area and usually spawns next to guards or other human enemies. This hostile dog will attack the player just like a regular enemy but is harder to hit because of its small hitbox and high agility.

The dog attacks by jumping towards its victim and biting them, dealing a full heart of damage, which is a lot for an area one enemy.

Overall the dog is an easy enemy that is difficult to avoid because of its wide field of view and high attention, but without humans around the dog is confused easily and will retreat.

Behavior
Like all enemies the dog roams its spawn area. It has an average view distance, but a large field of sight and high level of attention, allowing it to easily spot players.

Once alerted the dog will run towards its victim and attacking in melee. However, if the dog gets too far away from its initial start position and there are no living human enemies alerted the dog will randomly stop chasing its victim. This allows players to avoid killing dogs if they prefer not to do so.

Tactics
The easiest way to fight dogs is to simply take them down as soon as possible, preferably with shotguns, to make sure some bullets will hit, or fast-shooting small arms like revolvers, to be able to fire several rounds in short succession. Otherwise they will quickly notice and catch up to the player to attack.

A more peaceful way to handle hostile dogs is to avoid killing them alltogether. This is possible because they will stop chasing the player after some time, as long as there are no human enemies alive who also chase the player.

Trivia
The guard dog can easily be confused with the wild dog, which looks similar and is also a dog, but is not hostile.

It has not always been possible to avoid killing dogs. Only with Update 1.1 a mechanic to avoid aggroed dogs was added.