Daggerhawk

When you cast this spell on a ninmagical dagger, a ghostly hawk appears around the weapon. The hawk and dagger fly into the air and make a melee attack agaisnt on creature you can see within 60 feet, using your spell attack modifier and dealing piercing damage equal to 1d4 + your spellcasting ability modifier. On your subsequent turns, you can use a bonus action to cause the daggerhawk to attack again. 

The daggerhawk has AC 14 and, although it is invulnerable to damage, a successful attack against it sends the daggerhawk tumblilng, so it cannot attack again until after your next turn.