Dwarven War Hound (5e Creature)
From D&D Wiki
Dwarven War Hound
Medium beast, unaligned
These noble canines have been at the side of the dwarves throughout their troubled history. They serve the purpose not only for hunting but for guarding the village from outside beasts. During times of conflict, they are often used against cavalry. They will hide in the shadows and take down horses as they ride by. Although they are descended from standard mastiffs, selective breeding has led to war hounds being either black or gray and black spotted. It is not unusual to see the young children of the clan riding these dogs around the village.