Keen Hearing and Smell. The Fey wolf has advantage on Wisdom perception checks that rely on hearing or smell.

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

Bite. Melee Weapon Attack: +5, reach 5 ft., one target. Hit: 10 (3d4 + 2) piercing damage. If the target is a creature, it must succeed on a DC 13 Strength saving throw or be knocked prone. 

Scratch. Melee Weapon Attack: +3, reach 5 ft., one target. Hit: 13 (4d4) acid damage. If the target is a creature, it must succeed on a DC 15 Constitution saving throw each turn, take 1d4 damage every fail.

Lunge. Melee Weapon Attack: You may move 15 ft forward, if you encounter a creature while doing so you may use another action. You may use this once per 5 turns.

Maddening Speech. Ranged Spell Attack: The Fey Wolf may speak, it will speak in a tongue unknown but understood by all. Every creature who does not speak this tongue must roll DC 13 Wisdom Save, on fail you take 1d5 psychic damage, then targets roll with advantage DC 15 Wisdom Save, on fail they roll the Short-term Madness table 

Maddening Howl-

Once per long rest, the Fey Wolf can release a Maddening Howl. All target creatures within 50 ft must roll a DC 16 wisdom saving throw, on fail take 3d6 psychic damage and roll on the Short-term Madness table, on success take 1d6 psychic damage. If target fails saving throw multiple times from other attacks, roll on Long-term Madness table.