Afflicted Wolf

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.

Afflicted. The monster has the afflicted status. Attacks do additional necrotic damage that ignores resistance, and can only be healed through long rest.

Undead Fortitude. If damage reduces the wolf 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 wolf drops to 1 hit point instead.

Bite. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 10 (2d6 + 2) piercing damage. If the target is a creature, it must succeed on a DC 11 Strength saving throw or be knocked prone. If the target is not aflicted, it takes an additional (2d6) necrotic damage. This damage ignores all resistances, and cannot be healed magically.