What was once the heart of a Gemstone Dragon now serves as a specially crafted, magically protected receptacle.

A dark violet gem, laced with gleaming emerald veins running throughout. It's jagged form resembles a dragon's fang. You can choose to impale it into your form to have it imbue you with dark power.

At level 1, your life force is transferred into the stone. After you incapacitate a humanoid creature in combat by reducing it to 0 hit points you can remove the stone from your form as an Action for a number of turns equal to your level in order to impale that creature.

  Failing a charisma check against your spell save DC the humanoid duels you within the soul stone at half it's hit point maximum and with a penalty to it's AC equal to half your Character Level. Winning the duel sees the humanoid creature impaled, it's soul violently ripped apart, and it's body become your new vessel. Loosing the duel forces either subsequent duels with the creature or the return of the gem to your current form (your choice).

  This process causes you to loose a number of levels equal to the number of turns required to transfer your life force but not including duels. On a success, 1 ability score of your own is replaced with that of the humanoids. Your statistics and capabilities otherwise remain the same. Any equipment you are wearing or carrying remains borne by your previous form.

At level 3, You now have a resistance to poison. If you already have a resistance to poison you are now immune.

Additionally, When you attack a creature concentrating on a spell you can impose a penalty to their concentration check role equal to your Charisma modifier. 

At level 5, spells you cast (that would otherwise cost 1 action) can be cast as a bonus action on a creature that is under the effects of poison caused by you. 

At Level 7, As an Action you can shape change. You can magically polymorph into a humanoid equal to half your level in challenge rating, or back into your true form. You revert to your true form if you die. Any equipment you are wearing or carrying is absorbed or borne by the new form (your choice).

In a new form, you retain your alignment, hit points, Hit Dice, ability to speak, proficiencies, and Intelligence, Wisdom, and Charisma scores, as well as this action. Your statistics and capabilities are otherwise replaced by those of the new form, except any class features or legendary actions of that form.

At level 11, You now penetrate through any creatures resistance to poison damage caused by you. A creature that would otherwise have immunity to poison now has only resistance to poison damage caused by you. This ability does not apply to Constructs or Undead.

At level 15, You gain advantage on saving throws against spells and other magical effects and a unique Bonus to AC equal to half your Charisma Modifier for the purpose of avoiding spell damage entirely. Whenever you would normally be affected by a spell, you can choose to allow it to bypass your unique spell resistance AC, even when it is not your turn.

At Level 17, The Dragon Of Shadow grants you the power to turn magic back on its source. As a reaction when a spell that is targeting only you fails to overcome your unique spell resistance AC, you can reflect that spell back on the original caster, as if you were under the effect of a 9th level Counter Spell.

At Level 20, When you score a critical hit on a roll of 19 or 20, you roll the damage dice three times, instead of twice.

Notes: Bonus: Charisma Score, Bonus: Constitution Score, Bonus: Ability Score Maximum, Bonus: Ability Score Maximum, Bonus: Extra Attacks, Bonus: Hit Points per Level, Expertise: Stealth, Proficiency: Sleight of Hand, Expertise: Perception, Proficiency: Heavy Armor, Stacking Bonus: Strength Score, Remnant of Abraxas , Damage, Buff, Movement, Jewelry