Aberration (5A)

This is a Bogeyman subclass.

The stars are right! The sky rips apart and a thing that should not be steps through. The only one standing against this invasion is a lone monster rising to face the invader. This monster alone can stand against the maddening influence of what is even more alien!

Source: Original.

Twisted Mask

You are a humanoid on the outside, but inside a strange seed grows, a monstrous nature that comes out in moments of stress. Your creature type changes to aberration and your Dark Strike takes the shape of smashing limbs or tentacles, doing bludgeoning damage. You look is decided by your race and gender in the normal way—until you take damage and your body quite literally breaks open. This happens in three stages.

First Stage The first stage is your normal humanoid form. To casual observation you are a normal humanoid. Only those who come very close to you, physically or emotionally, can make a Wisdom (Insight) check against your Charisma (Deception) to sense that something is off about you, that you are an alien hiding under a humanoid skin. At stage one, you are resistant to poison and psychic damage and immune to the poisoned condition.
Second Stage You change into stage two when your Hit Points are reduced to half. Your skin now has visible cracks and splits showing not flesh but some alien substance. Your form shudders and twists, seeming to lack bones and a definite form. In dim light or at a distance of 30 feet, you still look roughly humanoid, but under better conditions any observer can notice your alien nature. You can walk among people as long as you are cloaked and do nothing to attract attention. At stage two, you are resistant to cold, poison, and psychic damage and immune to the poisoned and charmed conditions.
Third Stage If you lose all hit points you enter stage three. The change is dramatic, you shed your skin and a different creature emerges. This is your true form, and is up to you to describe. Common forms are bulbous, toadlike, insectoid, fungoid, or constantly morphing. Basically anything you can come up with, the more alien the better. At this stage, you provoke a extreme reaction from most humanoids, who are likely to either run away or attack you. At stage three, you are resistant to cold, lightning, poison, and psychic damage and immune to the charmed, frightened, and poisoned conditions.

Your form does not immediately return to normal when you recover hit points. Only after a long rest does your form return to stage one.

Escalating Vigor

At 3rd level, when you escalate from one stage of Twisted Mask to another, you can spend a Hit Die, roll the die, add your Constitution bonus and boogeyman level, and recover this many Hit Points.

Alien Toughness

At 6th level you gain resistance to bludgeoning, piercing, and slashing damage. Magical weapons ignore this resistance.

Sudden Escalation

Starting at 7th level, you can take a bonus action to instantly escalate the stage of your Twisted Mask ability by one step, from stage 1 to stage 2, or from stage 2 to stage 3. You do not take any damage doing this.

Escalating Horror

At 11th level when you take the Attack action, you gain an additional attack at stage 2 and two additional attacks at stage 3. When you use your Monster Scare ability, creatures that fail their saving throw also take psychic damage equal to your Dark Strike damage plus your Charisma modifier.

Alien Return

At 15th level, when you enter the third stage of your Twisted Mask you are infused with alien energy and recover all lost Hit Points. You can only do this once, and regain the ability at the end of a long rest.

Untouchable

When you reach 20th level, you gain resistance to all types of damage except necrotic and radiant damage.