It is common knowledge that warlock's make pacts with mysterious entities in order to learn and possess magical abilities. The patron could be fey nobles, demons, devils, hags, aliens, dragons, primordial, and many more. Some of these entities can either be living in the Materiel Realm, or reside within other dimension far from mortal reaches. However, this particular entity is far different from you usual patron, for it reside not on another realm, but instead within the warlock own body. This being is known as the "Parasite", a creature who origin is unknown to you, to where it came from or how you now have a living creature inside of you. The Parasite isn't a deity or a devil, and doesn't have much connection toward the Great Old One's residing in other realms. This creature is neither good or evil, it's only goal is to eat, grow and evolve to the point of becoming all powerful, and spreading forth it influences through it "offspring's"; in other words, making more parasites and infecting more people with it offspring's. As for the warlock, the Parasite telepathically speak through the mortal mind (though still within him), promising to teach him all form of magical abilities and other unique gifts, in exchange to help the Parasite to evolve along the way and spreading his offspring's upon the land.

The Parasite Expanded Spell List

The Parasite lets you choose from an expanded list of spells when you learn a warlock spell. The following spells are added to the warlock spell list for you.

 

The Parasite Expanded Spells

Spell Level	Spells
1st	inflict wounds, longstrider
2nd	detect thoughts, alter self
3rd	haste, vampiric touch
4th	vitriolic sphere, phantasmal killer
5th	cloudkill, telekinesis

Host of the Patron

Starting at 1st level, your body has been altered and improve by the Parasite living within your body, in order to help you survive better for your patron. You become resistances to both poison and acid-base attacks, due to having those essence now flowing through your vein by the parasite. You also possess the ability to Tremorsense sense, to which the range goes to about 60'ft. Lastly, your hit point maximum increases by 1 and increases by 1 again whenever you gain a level in this class.

 At 14th level, you now become immune to poison and acid damage.

Parasitic Offspring

Note: This ability only exist if you have chosen the "Pact of the Chain", otherwise this ability will not be available. At 3rd level, if you selected the Pact of the Chain, your patron create your very own familiar, causing this creature to burst out from your mouth and appear before you. This creature is known as a "Parasite", to which follow the rule of a familiar. The creature appear to look be a worm, yet it whole body is made from dozen of twisted tentacles. Despite is appearance, it is still capable to understand at least some form of languages, while using it tentacles to lift or carry items close to it size, though not able to wearing any kind of gears on it nasty form.

• -Tiny beast, unaligned
• -Armor Class: 12   (Natural Armor)
• -Hit Points:  7 (3d4)
• -Speed:  20 ft., burrow 40 ft.
• -STR: 5 (-3), DEX: 17 (+3), CON: 10 (0), INT: 7 (-2), WIS: 12(+1), CHA: 10 (0)
• -Skills: Stealth +5
• -Senses: Tremorsense 120 ft., Passive Perception 11
• -Languages: Common, Deep Speech 
• -Challenge: 1
• -Shapechanger. The parasite can use its action to polymorph into a beast form that resembles a bat (speed 10 ft. fly 40 ft.), a centipede (40 ft., climb 40 ft.), or a toad (40 ft., swim 40 ft.), or back into its true form. Its statistics are the same in each form, except for the speed changes noted. Any equipment it is carrying isn't transformed. It reverts to its true form if it dies.
• -Magic Resistance. The parasite has advantage on saving throws against spells and other magical effects.
• -Invisibility. The parasite magically turns invisible until it attacks or until its concentration ends (as if concentrating on a spell). Any equipment the parasite is carrying is invisible with it.
• -Bites (in Beast Form): Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 1 piercing damage.

The parasite only has one attack in it's true form, to which is known as "Parasitic Invasion." As an action, if your familiar is within 5'ft away from a target, it can dig through a target skin and live within it. For 1 minute, at the beginning of each of its turns, the target must constantly make a DC 15 Constitution saving throw. On a failed save, the target get disadvantage on attacks rolls and is deal 5 irreducible damage. Constructs, elementals, and undead automatically succeed this saving throw. At the end of this duration, or when the new host is reduced to 0 hit points, your parasite is ejected from the hosts body, and lands in a space adjacent to the creature. If you transfer your familiar to a host whose challenge rating is greater than your level, there is a 50% chance, at the DM's discretion, that the creature would be unaffected by the parasite, to which then the parasite dies off. If still alive after leaving the body, you can used your bonus action to summon the creature and devour it to gain hit points base of half the damages it causes to it host + warlock level, to which the parasite is consider dead till you cast the "Find Familiar" spell once more. You need a long rest to then used this ability again.

At level eight, if failing the Constitution saving throw, the damage now increase to 15 damage and the target become stunned till the end of it turn. At 14th level, when the target fails it saving throws, the target become paralyzed until the end of its turn, and takes 25 points of irreducible damage.

Venomous Overdose

At 6th level, when you cast a spell or use an ability that results in either poison or acid damage, you may ignore resistance's and deal half damage to foes with immunity to either acid or poison damage. Your two elemental-based attacks also gained an added damage of 1d6 + your Charisma modifier.

Symbiotic Mutation

Starting at 10th level, your Patron can altered your body in order to be suited for any situation you maybe find yourself in need to survive. With an action, you can choose one of the abilities below to be used for only one hour.

-Burrowing: You transform your hands and feets into a set of claws that are design to dig through the ground and break through rocks with ease. You can travel up to 40'ft speed beneath the ground, and with the aid of Tremorsense give you the ability to feel the vibration on the ground.

-Flying: You can grow large, leathery wings that will grant you the ability to fly. You have 40'ft speed in the air. You can’t manifest your wings while wearing armor unless the armor is made to accommodate them, and clothing not made to accommodate your tentacles might be destroyed when you manifest them.

-Tentacles: You can grow to possessing two, long appendages that allow you to climb up wall and ceiling with ease, with only 30'ft speed. You can’t manifest your tentacles while wearing armor unless the armor is made to accommodate them, and clothing not made to accommodate your tentacles might be destroyed when you manifest them.

You can used these abilities for only one time. The effect end if an hour passed, or using an action to stop it early. You need to get a short-rest to gain back the abilities.

Parasitic Evolution

At 14th level, as an action, you can allow your patron to cause your body to undergo a horrific transformation. Parasitic tentacles wrap around the warlock whole body to form a slimly, cocoon, to which then burst open and reveal a monstrous creature within. You become an humanoid creature (Large-size) that has toned, leaner physique. The head become more skull-like with a lipless grin, most of it body is cover in exoskeleton, and having four long, muscular appenages that each possess a long, curve scythes at the end. For the duration of 1 minute, you gained the following abilities:

• -You become resistance to bludgeoning, piercing or slashing damage that are non-magical, and gain an added + 3 AC.
• -When you are attempting to attack, you get the added attack bonus from your Charisma modifier, instead of relaying on your Strength modifier.
• -When transform, you start off with maximum HP, with temporary hit points equal to half your hit point maximum. When you revert to your normal form, you return to the number of hit points you had before you transformed. However, if you revert as a result of dropping to 0 hit points, any excess damage carries over to your normal form. For example, if you take 10 damage in your monstrous form and have only 1 hit point left, you revert and take 9 damage. As long as the excess damage doesn’t reduce your normal form to 0 hit points, you aren’t knocked unconscious. 
• -You are consider to be Monstrous. As such, you are unable to speak, only making growling noise.
• -You can’t cast spells while in this form. This form also breaks whatever concentration spell you were maintaining. This form requires concentration to maintain.
• -Your equipment merges with you during your transformation, but is unusable while in this form.
• -You possess claws on both hands and feet's, design only to burrow and climb up to 40'ft in this form, not to fight.
• -You possess four long, spider-like appendages that reach up to 10 feet, with scythe-like ends that are coated with acid. As an action, you can use up to four attacks that deals 1d8 slashing and 1d8 acid damage each (total to 4d8 slashing and 4d8 acid).
• -As an action, you can used your very own ability, known as "Parasite Plague". A swarm of tiny parasite's that secreted out from your body and fill a 20-foot-radius sphere centered on a point you choose within the range of 300. The sphere spreads around corners. The sphere remains for the duration of the form (less then one minutes), and its area is lightly obscured. The sphere's area is difficult terrain. When the area appears, each creature in it must make a Constitution saving throw. A creature takes 3d10 piercing damage and 3d10 poison damage on a failed save, or half as much damage on a successful one. A creature must also make this saving throw when it enters the spell's area for the first time on a turn or ends its turn there. This ability only work one time in battle and can't be used again afterward till the end of the transformation.

The transformation end when one minutes are up, spend an action to end it early, or if you become unconscious. You then need to spend a long-rest to gain the ability back.