Frumious Quills of the Bandersnatch (Warlock Invocation)

The incandescent fury and wickedly-barbed quills of a raging, fairy-tale monster churn deep inside you … and, with a roar, you can let them rip-forth in a tremendous cascade. When you use eldritch blast, you can impale your target, changing the damage type to magical piercing. A creature that takes damage must make a Dexterity saving throw; on a failure, the target is stuck with 1d4 quills. As long as the target has quills impaled in them, the creature has disadvantage on attack rolls and ability checks. Removing a quill requires a Wisdom (Medicine) check against your spellcasting DC; success removes one quill, plus an additional quill for every 5 points by which the check succeeds. Once removed, a quill swiftly fades back into ash and nothingness. This invocation cannot be used in conjunction with an invocation that changes the base damage of eldritch blast to a damage type other than piercing.