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

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

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.

Undead Nature. A zombie doesn't require air, food, drink, or sleep.

Bite. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 7 (2d4 + 5) piercing damage. If the target is a creature, it must succeed on a DC 11 Strength saving throw or be knocked prone.