Archibald

Shapechanger. Archibald can use its action to polymorph into a beast form that resembles a falcon (20 ft., fly 60 ft.) or back into his true form. Its statistics are the same in each form, except for the speed changes noted. Any equipment he is wearing or carrying isn't transformed. He reverts to its true form if he dies.

Magic Resistance. Archibald has advantage on saving throws against spells and other magical effects.

Familiar.  Archibald has formed a pact with Augustus during his time trapped in the Feywild to serve him as a familiar, forming a telepathic bond between them. While the two are bonded, the master can sense what Archibald senses as long as they are within 1 mile of each other. While Archibald is within 10 feet of its master, the master shares Archibald's Magic Resistance trait. If its master violates the terms of the contract, Archibald can end its service as a familiar, ending the telepathic bond.

Claws (in beast form) . Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 5 (1d4 + 3) slashing damage, and the target must make a DC 11 Constitution saving throw, taking 10 (3d6) poison damage on a failed save, or half as much damage on a successful one.

Shortbow (in true form). Ranged Weapon Attack: +6 to hit, range 40/160 ft., one target. Hit: 5 (1d4+3) piercing damage, and the target must succeed on a DC 11 Constitution saving throw taking 10 (3d6) poison damage on a failed save, or half as much damage on a successful one.

Invisibility. Archibald magically turns invisible until it attacks or until its concentration ends (as if concentrating on a spell). Any equipment Archibald wears or carries is invisible with it.

Fey Step. As a bonus action, Archibald can teleport up to 30 feet to an unoccupied space it can see. He must take a long rest after teleporting in this way before he's able to do it again.