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

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.

Bite. Melee Weapon Attack: +1 to hit, reach 5 ft., one target. Hit: 4 (1d6 + 1) piercing damage.
Teleport (Recharge 6). The dog magically teleports, along with any equipment it is wearing or carrying, up to 20 feet to an unoccupied space it can see. Before or after teleporting, the dog can make one bite attack.