Companion Hound

Beast of the Hunt. The companion hound is a capable hunter, and is magically enhanced in ways that make finding prey easier. It innately possesses the ability to cast Hunter's Mark at 1st level up to 3 times per day. 

Keen Hearing and Smell. The companion hound has advantage on Wisdom (Perception) checks that rely on hearing or smell.

Pack Tactics. The companion hound has advantage on an attack roll against a creature if at least one of its allies is within 5 feet of the creature and the ally isn't incapacitated.

Enlarge (2/Day). The companion hound barks three times, increasing in size until it is considered a large creature. All creatures within 30 feet who can see it and are size medium or smaller must succeed a DC 11 Wisdom saving throw or be frightened for 1 minute. While enlarged, whenever the companion hound attacks it uses the enlarged bite attack instead of its usual bite attack and the enlarged claw attack instead of it usual claw attack. Additionally, its Strength score increases by +4, his AC by +2, and its hitpoint maximum triples. This effect lasts for 1 minute. 

Multiattack. The companion hound makes two attacks, one with its bite and with its claws (if it is enlarged, it uses the enlarged variants of these attacks). 

Bite. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 5 (1d6 + 2) piercing damage. If the target is a creature, it must succeed a DC 12 Strength saving throw or be knocked prone. 

Claw. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 4 (1d4 + 2) slashing damage.

Enlarged Bite. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 14 (3d6 + 4) piercing damage. If the target is a creature, it must succeed on a DC 14 Strength saving throw or be knocked prone.

Enlarged Claw. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 11 (3d4 + 4) slashing damage.