Assaulting Shadows

Your body, upon taking damage, is engulfed in black ghostly shadows and you step back 5ft if possible, leaving those shadows in place of where you were stood. This does not provoke a attack of opportunity from any means (including sentinel). The target must then make a dexterity saving throw against the shadows, on a hit the target takes 1d4 psychic damage.

Assault.
You may make additional attacks if you choose, each attack increasing by dice type, 1d6, 1d8, 1d10, 1d12 and finally up to 1d20. However each attack after the 1d4 attack role will force you to make a constitution saving throw of DC12 + number of additional attacks after the first, on a fail you take one level of exhaustion.

Table.
1st attack: 1d4
2nd attack: 1d6
3rd attack: 1d8
4th attack: 1d10
5th attack: 1d12
6th attack and onwards: 1d20

When cast at a higher level (6th or higher) you roll two of each dice per attack.