Armor Class 12
Hit Points 5 (1d8 + 1)
Speed 40 ft.
Skills Perception +3
Senses passive Perception 13
Languages —
Challenge 1/8
Keen Hearing and Smell. The mastiff has advantage on Wisdom (Perception) checks that rely on hearing or smell.
Bite. Melee Weapon Attack: +3 to hit, reach 5 ft., one target. Hit: 4 (1d6 + 1) piercing damage. If the target is a creature, it must succeed on a DC 11 Strength saving throw or be knocked prone.
Monster Manual (2014), p. 332