Blood Wolf

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

Vampiric. Although they can survive without food or water, they must feed on fresh blood at least once a month. While in direct sunlight, a blood wolf has disadvantage on attack rolls and ability checks.

Blood Frenzy. Advantage on attack rolls against any creature that doesn't have all its hit points.

Regeneration. The wolf regains 8 hit points at the start of its turn if it has at least 1 hit point, isn't in direct sunlight, and did not take radiant or holy damage in the previous turn.

Bite. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 8 (2d4 + 3) piercing damage plus 1d6 necrotic damage. If the target is a creature, it must succeed on a DC 13 Strength saving throw or be knocked prone. The target's hit point maximum is reduced by an amount equal to the necrotic damage taken, and the blood wolf regains hit points equal to that amount. The reduction lasts until the target finishes a long rest.

Howl (Recharge 5-6). The blood wolf bays an anguished howl. The noise has no effect on constructs or undead. All other creatures within 30' who hear it must succeed on a DC 12 Wisdom check, or be Frightened. The DC is increased by 2 for each additional blood wolf that joins in, but only one save is needed against all howls. If outdoors, each howl will summon 1d4-1 (normal) wolves which will arrive in 1d4 rounds.