Larva Mage

The Material Plane represents only one small part of the multiverse. Beyond the best-known planes of existence lie realms that are lethal to mortal life. Some are so hostile that even a moment’s contact with such a place is enough to plunge a mortal mind into madness. Yet beings do exist that are native to these realms: beings that are eternally hungering, searching, warring, sometimes dreaming. These Elder Evils are far older than most of the mortal races and always horrific to humanoid minds.

However much they might desire to enter and dominate the Material Plane, the Elder Evils are unable or unwilling to leave their realms. Some are imprisoned in their dimensions by external forces, some are inextricably bound to their home realities, and others simply can’t find any way out. 

A larva mage is a nightmarish combination of a mortal body and otherworldly substance. When a powerful cultist of a wormlike entity such as Kyuss or Kezef  contacts the comet-borne emissary of an Elder Evil, the emissary can merge with a mortal consciousness to create a larva mage. Your personality survives the transformation, altered, mostly alien.

Other Worldly Nature

Your link to the Elder Evils allows you to You can speak, read, and write Deep Speech.

At 1st level, you learn the Eldritch Blast cantrip. It counts as a sorcerer cantrip for you, but it doesn't count against your number of cantrips known.

Return to Worms

Starting at 1st level, your body is imbued with a mass of wriggling larva making you difficult to defeat. When damage reduces you to 0 hit points, you can make a Charisma saving throw (DC 5 + the damage taken). On a success, you instead drop to 1 hit point. You can’t use this feature if you are reduced to 0 hit points by a critical hit.

After the saving throw succeeds, you can’t use this feature again until you finish a long rest.

Hive Mind

At 6th level, you gain resistance to psychic damage.

Feed on Weakness

When a creature within 30 feet of the you fails a saving throw from one of your spells or abilities, you gain temporary hit points equal to 1d6 + your Charisma modifier.

You may benefit from this effect once per turn from only one creature.

Plague of Worms

Starting at 14th level you can spend 5 sorcery points to hurl a Swarm of worms and maggots. Each creature of your choice within 15 feet of the you must succeed on a Dexterity saving throw or take 5d8 necrotic damage. The affected creature takes 2d8 necrotic damage at the start of each of your turns. The creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Aura of Madness

Beginning at 18th level, you can channel the insanity of your ancestor causing enemies around you to doubt their existence. As an action you can spend 7 sorcery points to draw on this power to exude an aura of madness to a distance of 30 feet. For one minute or until you lose your concentration (as if you were casting a concentration spell) each hostile creature that starts its turn in the aura must succeed on a Wisdom saving throw or have disadvantage on saving throws, as well as on attack rolls against creatures until the aura ends. A creature that succeeds on this saving throw is immune to your aura for 24 hours.