Multiattack

The ankou can use its Horrifying Presence. It then makes three attacks: one with its bite and two with its claws.

Bite

Melee Weapon Attack: +14 to hit, reach 15 ft., one target. Hit: 18 (2d10 + 7) piercing damage plus 11 (2d10) cold damage.

Claw

Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 14 (2d6 + 7) slashing damage.

Tail

Melee Weapon Attack: +14 to hit, reach 20 ft., one target. Hit: 16 (2d8 + 7) bludgeoning damage.

Horrifying Presence

Each creature of the ankou's choice that is within 120 feet of it must make a DC 19 Wisdom saving throw. On a failure, its speed is reduced to 0 for 1 minute. If the save fails by 5 or more, the creature is instead paralyzed for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the ankou's Horrifying Presence for the next 24 hours.

Reaper's Breath (Recharge 5-6)

The ankou exhales cold fire in a 120-foot line that is 10 feet wide. Each creature in that area must make a DC 22 Dexterity saving throw, taking 66 (12d10) cold damage on a failed save, or half as much damage on a successful one. Undead creatures automatically fail the saving throw and treat all damage dealt by this breath weapon as radiant instead of cold.

Change Shape

The ankou magically polymorphs into any beast, humanoid, or undead creature it has seen before that has a challenge rating no higher than its own, or back into its true form. It reverts to its true form if it dies. Any equipment it is wearing or carrying is absorbed or borne by the new form (the ankou's choice). Its statistics, other than its size, are the same in each form and it doesn't gain any class features or legendary actions of the new form.

Usher of Souls

The ankou can transport itself and up to eight creatures in contact with it to another plane of existence. This works like the plane shift spell, except dead or incorporeal creatures can be transported and don't have to be willing. The ankou can't use this ability to banish an unwilling creature.