The Great Old One: (warlock patron variant)

Intelligent Spell-casting (level 1)

Instead of having charisma as your spell-casting ability for your warlock spells, you can instead use your intelligence to cast spells with. In addition to that, any invocation which uses your charisma modifier to determine its effects can instead use your intelligence modifier. Whenever you gain a level in any class you can decide to activate or deactivate this feature.

Additional Spells (level 1)

The Great old one 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.

Great Old One Expanded Spells

Spell Level	--- Spells
1st	Dissonant Whispers, Tasha's Hideous Laughter
2nd	Detect Thoughts, Phantasmal Force
3rd	Blink, Clairvoyance
4th	Confusion, Phantasmal Killer
5th	Dominate Person, Dream

Visions of the Other Worlds (level 1)

Every night, your dreams are haunted by the sight of abominations of arcane origins. You have began to analyze and learn more about these monsters. Whenever you make an intelligence check to re-call information about or relating to aberrations, fiends, monstrosities, oozes or undead, you have advantage on the check.

If you spend at least 1 minute recalling information about a creature of any those types outside of combat, then you automatically learn its damage vulnerabilities, resistances and immunities alongside any condition immunities it has.

Deranged Whispers (level 6)

Whenever a creature targets you with an attack roll you can use your reaction to magically generate a disturbing cacophany of discordant gibbering, screaming and crying. Until the beginning of your next turn, attack rolls against you are made with disadvantage.

Once you use this feature, you cannot use it again until you complete a short or long rest.

Enhanced Telepathy (level 10)

You can communicate telepathically with any creature within 120 feet of you. You don't need to share a language with the creature for it to understand your telepathic utterances, but the creature must be able to understand at least one language. Whenever you telepathically communicate with a creature, they can reply to you using telepathy, but they can only do so directly after you state your message.

You can use your action to establish a telepathic bond with a willing creature that you have been within 120 feet of for at least an hour. A bonded target can telepthically communicate with you beyond any distance, even if you are on different planes of existence. A bonded target can send telepathic messages to you at any time. You can only be bonded with one creature at a time. This bond ends whenever you use this feature to create a bond with another creature, or if you consciously decide to drop it (no action required)

Pyschic Drain (level 14)

You can use a bonus action on your turn to target a creature within 60 feet of you who you can see and who is under the effects of an enchantment, illusion or necromancy spell cast by you. That target takes 2d6+1 psychic damage and you gain an amount of temporary hit points equal to the damage dealt by this feature. If the creature gets to remake a saving throw to resist a spell whenever it takes damage, than it has disadvantage on the roll when trigerred by the damage of this feature.

You can use this feature up to a number of times equal to your intelligence or charisma modifier (minimum of once). Whichever ability score this uses corresponds to what your warlock spell-casting ability currently is. All expended uses are regained after you complete a long rest.