Keen Hearing and Smell. The mastiff has advantage on Perception checks that rely on hearing or smell.
Maneuvers. The mastiff uses maneuvers (maneuver save DC 12). It has 2 stamina dice which are d8s, a dice limit of 1, regains all expended stamina dice when it finishes a long rest, and regains half its total stamina dice when it finishes a short rest. It knows the following maneuvers:
Bite. Melee Weapon Attack: +3 to hit, reach 1 m. Hit: 4 (1d6 + 1) piercing damage.
As an action, you can make a melee weapon attack and a Brawn check to grapple the creature.
You can add the stamina die to the attack’s damage (add half if you miss by 4 or less) for each additional stamina die expended.
As an action, you can use the Dash action. If you move at least 4 meters straight toward a creature, you can make a melee weapon attack against it. Add the stamina die to the attack’s damage (add half if you miss by 4 or less).
You can increase the damage for each additional stamina die expended.