The Hydra

The patron of this archetype is a Poison Hydra. You take on the poisonous traits, and some of the hydra traits from your patron.

Poison

At 1st level, you can use your action to make a creature do a Constitution saving throw (Spell Save DC), and on a fail the creature is poisoned for a minute. On each of its turns, it can use its action to redo the saving throw; on a success, it ends the poisoned condition early. This ability has an amount of charges equal to your Charisma modifier, and you regain these after a long rest.

Poison Expert

At 6th level, choose one of the following abilities to gain:

No Safe Havens

Your attacks and spells ignore poison resistance and immunity, and immunity to the poisoned condition.

Poisonous

You gain immunity to poison and necrotic damage and the poisoned condition. Additionally, when creatures attack you with a melee attack, they take 1d4 poison damage.

Hydra’s Wrath

At 10th level, choose one of the following abilities to gain:

Hydra’s Avatar

You accept the Hydra becoming its avatar so you gain its features. Your creature type becomes aberration, your size becomes large (unless if you’re already large or are larger), and you gain a total of five heads. While you have more than one head, you have advantage on saving throws against being blinded, charmed, deafened, frightened, stunned, and knocked unconscious.
Whenever you take 25 or more damage in a single turn, one of your heads dies. If all your heads die, you die.
At the end of your turn, you grow two heads for each head that died since your last turn; however, if you take fire or radiant damage, you cannot regain heads for a minute. You regain Charisma modifier (minimum 1) amount of hit points for each head regrown in this way.

Hydra’s Breath

You can use your action to spray the poison breath of your patron into the air, and let it fall around you onto the battlefield. Creatures within 15 ft. of you must make a Dexterity saving throw (Spell Save DC). On a fail, a creature takes 6d6 poison damage, and takes 1d4 poison damage on the beginning of their turns for 1 minute. On a success they take half of the 6d6 poison damage, and don’t take the over time damage. This feature has one charge per long rest.

Imbued Power

As a bonus action, you can touch a weapon to imbue it with the power of your patron for a minute. When a creature gets hit with an attack from weapon, they take 1d6 poison damage and must make a Constitution saving throw. On a fail, a creature becomes poisoned until your next turn. This feature has one charge per long rest.

Purple Mist

You can use your action to summon a purple mist on yourself or weapon that has the same effects as Darkness; however, creatures that start their turn within it take 1d4 poison damage, and have disadvantage on Constitution saving throws. This purple mist you are able to see through, and you can use a bonus action to allow up to 3 other creatures to see through it. This feature has an amount of charges equal to your Charisma modifier that you regain after a long rest.

Mastery of Poison

At 14th level, choose one of the following abilities to gain:

Chain Poison

You can use your action to make up to three creatures within 30 ft. do a Constitution saving throw (Spell Save DC). On a fail, a creature becomes poisoned, and takes 2d6 poison damage on the beginning of its turns. On each of its turns, a creature can use its action to redo the saving throw; on a success, it ends the poisoned condition early. This ability has one use that you regain after a long rest.

Descent of the Hydra

As an action you’re able to summon your patron upon the mortal plane. A Hydra descents upon the battlefield. The Hydra goes right after you in initiative, and you communicate with the Hydra telepathically to tell it what to attack (requires no action). If given no request, the Hydra will attack the closest creature excluding you. When the Hydra reaches 0 hit points, it returns to the realm it came from. The Hydra only stays with you for 1 hour, and this ability has one charge per long rest.

Poisonous Rain

You can use your action to create a poisonous cloud that takes up a 30 ft. radius. Whenever a creature enters this radius for the first time or starts their turn within it, the creature takes 10 poison damage. This cloud last for 1 minute, and this ability has one use per long rest.