Shapechanger. The wereowl can use its action to polymorph into an owl-humanoid hybrid or into a giant owl, or back into its true form, which is humanoid. Its statistics, other than its size, are the same in each form. Any equipment it is wearing or carrying isn't transformed. It reverts to its true form if it dies.

Arcane Weapons. The wereowl's attacks that use a weapon are magical, and it can use its Intelligence modifier, instead of Strength or Dexterity, for the attack and damage rolls. When the wereowl hits with such an attack, the weapon deals an extra 2d4 force damage (included in the attack).

Flyby (Owl Form Only). The wereowl doesn't provoke opportunity attacks when it flies out of an enemy's reach.

Innate Spellcasting (Humanoid or Hybrid Form Only). The wereowl's innate spellcasting ability is Intelligence (spell save DC 13, +5 to hit with spell attacks). The wereowl can innately cast the following spells:

At will: mage hand, message, minor illusion, prestidigitation, ray of frost
2/day each: detect magic, disguise self, invisibility, magic missile, sleep
1/day: dimension door

Keen Hearing and Sight. The wereowl has advantage on Wisdom (Perception) checks that rely on hearing or sight.

Multiattack (Hybrid Form Only). The wereowl makes one attack with its beak and one attack with its quarterstaff. It can cast a spell in place of one of these attacks.

Beak (Owl or Hybrid Form Only). Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 5 (1d4 + 3) piercing damage. If the target is a humanoid, it must succeed on a DC 11 Constitution saving throw or be cursed with wereowl lycanthropy.

Talons (Owl Form Only). Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 8 (2d6 + 3) slashing damage.

Quarterstaff (Humanoid or Hybrid Form Only). Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 7 (1d6 + 3) bludgeoning damage, or 8 (1d8 + 3) bludgeoning damage if used with two hands, plus 5 (2d4) force damage.

Ray of Frost (Cantrip, Humanoid or Hybrid Form Only). Ranged Spell Attack: +5 to hit, range 60 ft., one target. Hit: 9 (2d8) cold damage, and the target's speed is reduced by 10 feet until the start of the wereowl's next turn.