Void Weapon

You create a spectral weapon in your hand or within range that lasts for the duration or until you cast this spell again. When you cast the spell, you can make a melee spell attack against a creature within 5 feet of the weapon. On a hit, the target takes necrotic damage equal to 1d8 + your spellcasting ability modifier.

As a bonus action on your turn, you can move the weapon up to 20 feet or back in your hand and repeat the attack against a creature within 5 feet of it.

The weapon can take whatever form you choose. 

At Higher Levels. When you cast this spell using a spell slot of 3rd level or higher, the damage increases by 1d8 for every two slot levels above 1st.