Spectral Cleave / Penetrating Shot

As the serum takes effect, you feel a strange sensation in your hands.  When you hold an item in your hand, by focusing on this sensation, you are able to temporarily turn that item into a spectral version of itself.  You can activate this ability as a bonus action on your turn, transforming a weapon in your hand into a spectral form which lasts until the end of your turn.  Your transformed weapon is able to pass smoothly through matter, allowing you to attack multiple enemies with a single attack. 

You may use this ability a number of times equal to your proficiency bonus plus one, per short rest.

If you transformed a melee weapon, you can make an attack against a foe within reach that cleaves into other foes. If you hit, you deal damage normally and can make an additional attack (no action required) against one other foe that is also within your reach. You may only use this cleave attack once on your turn.

If you transformed a ranged or thrown weapon, you can make an attack against a foe within range that pierces through into foes behind. If you hit, you deal damage normally and can make an additional attack (no action required) against one other foe that is in a straight line behind the initial foe and within your range. You may only use this extra piercing attack once on your turn.