Magic Resistance. The owlbear has Advantage on saving throws against spells and other magical effects.

Wraith's Flight. The owlbear does not provoke opportunity attacks when using its fly speed.

Multiattack. The owlbear makes two Killing Blow attacks.

Killing Blow. Melee Attack Roll: +10, reach 5 ft. Hit: 16 (2d8 + 7) Slashing damage plus 6 (2d6) Necrotic damage. On a hit, the target must make a DC 13 Constitution saving throw. On a failure, the creature's hit point maximum is reduced by the number of necrotic damage it took as part of this attack. If this attack would bring a creature's hit point maximum to zero, they die. A creature whose hit point maximum was reduced in this way recovers 1d10 of their hit point maximum after each long rest until they reach their original hit point maximum. A creature who is affected by the Lesser Restoration spell instantly regains 1d10 of their maximum hit points. A spell like Greater Restoration or Wish instantly restores the creature's hit point maximum.

Chilling Breath (Recharge 5–6). Constitution Saving Throw: DC 15, each creature in a 20-foot Cone originating from the owlbear. Failure: 14 (3d8) Cold damage plus 14 (3d8) Necrotic damage, and the target has their movement speed reduced by 10 ft. until they are magically healed or take a long rest. Success: Half damage only.

Bone Form. The owlbear loses  its more ethereal properties and becomes much more physical and skeletal. The owlbear's AC decreases by 2 but the necrotic damage dealt by its Killing Blow increases by 2d6. The owlbear can revert to its normal form by using this Bonus Action again.

Ethereal Retreat. When the owlbear takes damage from a weapon attack or spell, it can use its reaction to move to the Ethereal Plane. It can move back to the Material Plane on its turn using a Bonus Action. The owlbear cannot use this feature while in its Bone Form.