You plunge your teeth into one humanoid you can see (non-boss) within 5' once per long rest and drain 50% of their current health. 

Every time you transform, you lose a bit of yourself but become stronger. When you transform, roll a D20, If you roll lower or equal to your level /3 rounded down, you become inflicted with madness for 3 turns and this cannot be dispelled, cured, etc. You get to increase an ability score of your choice by 2. 

All of your ability scores increase by 1

Changelings mature slightly faster than humans but share a similar lifespan—typically a century or less. While a changeling can transform to conceal their age, the effects of aging affect them similarly to humans.

Entities are the embodiment of fear and terror. These creatures are almost always chaotic evil. 

Your size is Medium. To set your height and weight randomly, start with rolling a size modifier:

Size modifier = 2d4

Height = 5 feet + 1 inch + your size modifier in inches

Weight in pounds = 115 + (2d4 × your size modifier)

Your base walking speed is 30 feet.

As an action, you can change your appearance and your voice. You determine the specifics of the changes, including your coloration, hair length, and sex. You can also adjust your height and weight, but not so much that your size changes. You can make yourself appear as a member of another race, though none of your game statistics change. You can’t duplicate the appearance of a creature you’ve never seen, and you must adopt a form that has the same basic arrangement of limbs that you have. Your clothing and equipment aren’t changed by this trait.

You stay in the new form until you use an action to revert to your true form or until you die.

Your proficiency bonus increases by 1

You  can see in the dark up to 30'