Expecto Patronum

You create a floating, spectral creature 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 spectral creature it can also attack creatures on the ethereal and astral plane. On a hit, the target takes radiant damage equal to 1d8 + your spellcasting ability modifier. or 1D10 + your spellcasting ability modifier against fiends and undead  

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

The creature can take whatever form you choose. 

At Higher Levels. When you cast this spell using a spell slot of 5rd level or higher, the damage increases by 1d8 (1D10 against fiends and undead) for every level above 4th level.