Multiattack

The ankou makes three attacks: one with its bite and two with its claws.

Bite

Melee Weapon Attack: +6 to hit, reach 10 ft., one target. Hit: 14 (2d10 + 3) piercing damage plus 4 (1d8) cold damage.

Claw

Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 10 (2d6 + 3) slashing damage.

Reaper's Breath (Recharge 5-6)

The ankou exhales cold fire in a 30-foot line that is 5 feet wide. Each creature in that area must make a DC 15 Dexterity saving throw, taking 44 (8d10) 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.