Aethertail

Keen Sight. Aethertale has advantage on Wisdom (Perception) checks that rely on sight.

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

Evasion. If an Aethertail is subjected to an effect that allows it to make a Dexterity saving throw to take only half damage, then it instead takes no damage if it succeeds on the saving throw, and only half damage if it fails.

Flyby. Aethertail doesn't provoke opportunity attacks when it flies out of an enemy's reach.

Freedom of Movement. Aethertail's ignores difficult terrain, and magical effects can't reduce its speed or cause it to be restrained. It can spend 5 feet of movement to escape from nonmagical restraints or being grappled. 

Dashing Ferocity. Whenever Aethertail makes the dash action, it rolls twice as many dice to determine damage until the end of its initiative turn. 

Familiar Navigation. If an Ather tail is a familiar for a character, if they spend a long rest together, Aethertail always knows the location of the character as long as their on the same plane of existence.

Multiattack. Aethertail can take two attacks in an attack action, one with its beak and one with its claws.

Beak. Melee Weapon Attack: +4; to hit, reach 5 ft., one target. Hit: 5 (1d6 + 2); piercing damage.

Claws. Melee Weapon Attack: +4; to hit, reach 5 ft, one target. Hit 7 (1d8 + 2)  

Misty Flight. Can cast Misty Step as an action, 3 times a day.

Invisibility. Can cast invisibility as an action, 1 time per day.

Cunning Action. Aethertail's can take a bonus action on each of its turns in combat. This action can be used only to take the dash, dodge, or hide action.

Extra Swing. Aethertail can make a melee attack with its claws as a bonus action.

Desperate Escape. As a reaction to reaching 0 hit points, Aethertail instead drops to 1 HP and turns invisible and dashes in any direction.