The Phantom-Striker

A phantom-striker warlock makes a pact with a powerful, ghostly being. This being could be the restless spirit of a long dead archmage, a particularly generous demilich, or anything that has powers beyond that of a physical form. Phantom-strikers are gifted abilities that mimic the ethereal nature of their patrons, enhancing their movement and combat capabilities. These abilities could allow them to pass through objects, attack through their opponent's defenses, or give them abjuration or illusion abilities. 

Ghostly Pass

Starting at 1st level, you can, for a brief moment, make your body ethereal enough to pass through some objects. You can use this ability during movement to pass through objects or creatures that are no more than 5 feet across. If this etherealness ends while you are inside of an object, you are violently ejected to the last point you were at before you entered the object, and you take 2d10 force damage. You can use this ability more than once per turn, but you cannot use it consecutively to increase the distance that you move while under the abilities effects, and it can only be used an amount of times per day equal to your Charisma modifier.

Expanded Spell List

1st Level: Disguise Self, Silent Image

2nd Level: Blur, Spiritual Weapon

3rd Level: Nondetection, Phantom Steed

4th Level: Freedom of Movement, Greater Invisibility

5th Level: Mislead, Seeming

Ghostly Strike

Starting at 6th level, you can alter a weapon or spell attack you make to briefly turn ethereal, allowing it to breach its targets defenses. You can use a bonus action when making a weapon or spell attack roll to increase the attack's chances of hitting. The target's AC is treated as 10 + its Dexterity modifier, unless the creature has an ability that would negate this effects, and the attack isn't affected by any effect caused by the target's armor, like the rust effect of a rust monster or a Tarrasque's reflective carapace. Once this ability is used, it cannot be used again until you finish a short or long rest. 

Shadow Morph

Starting at 10th level, you adopt the ability to levitate of spirits and specters. As a bonus action on your turn, you can turn your legs into dark clouds, getting rid of your ability to walk, but giving you flying speed equal to your prior movement speed. This ability lasts for 1 minute, or if you end it as a bonus action. Alternatively, you can forgo the flying speed and instead give yourself the effects of the Etherealness spell for a minute, or if you end it as a bonus action. 

If either of these abilities are used, neither can be used until you finish a long rest. 

Pass of the Phantasma

Starting at 14th level, you can harness your ability to pass through creatures for offensive purposes. When you use your Ghostly Walk ability to pass through a creature, you can create a surge of energy through your body that harms the creature that you walk through. The target must make a Constitution saving throw, taking 3d10 force damage on a fail, and half on a  success.