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

Pack Tactics. The dog has advantage on attack rolls against a creature if at least one of the dog's allies is within 5 feet of the creature and the ally isn’t incapacitated.

Pounce. If the dog moves at least 20 feet straight toward a creature and then hits it with a bite attack on the same turn, that target must succeed on a DC 12 Strength saving throw or be knocked prone.

Undead Fortitude. If damage reduces the zombie to 0 hit points, it must make a Constitution saving throw with a DC of 5 + the damage taken, unless the damage is radiant or from a critical hit. On a success, the zombie drops to 1 hit point instead.

Stench of Death. Each creature that starts its turn within 10 feet of the zombie dog must make a DC 14 Constitution saving throw, unless the creature is a construct or undead. On a failed save, the creature is incapacitated until the end of the turn. Creatures that are immune to poison damage or the poisoned condition automatically succeed on this saving throw. On a successful save, the creature is immune to the stench of all corpse flowers and their zombies for 24 hours.

Bite. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 4 (1d6 + 1) piercing damage.

Retriever of Death. If unthreatened, the zombie dog causes one unsecured, unconscious humanoid within 5 feet of it to be grappled and each turn attempts to drag the creature up to half its movement toward its master, along with any equipment the creature is wearing (or carrying, if rigor mortis is present).

That's My Girl.  When a creature the dog can wee within 5 feet of it makes an attack action against at least one of the dog's allies, it can use its reaction to make a bite attack against that creature. Before the attack is rolled, the target may choose to take an automatic hit, suffering the damage but maintaining any concentration. Otherwise, a successful attack roll imposes disadvantage on the target's attack roll.