The Arcane

Your Patron is an 18th level or higher arcane spellcaster. Sometimes even great wizards and sorcerers need fuel for their spells and experiments. When this happens, some have no problem making arcane deals for spell components. Need a soul for a spell? Need someone indebted to you? Need someone to test that really dangerous spell you wrote? These are all ways that a spellcaster would make a pact with someone to give them power. In some circumstances, it is entirely to help them, but in other ways, this is a fantastic way to push yourself, or gain a following. Being in-debted to a spellcaster sometimes is just as dangerous as getting power from a higher entity. The emotions of wizards and sorcerers are fickle, and they do not need to abide by most rules since they are mortals with great power. You would do best not to double-cross them.

Alternate feature

This subclass functions as a Charisma caster. If you would like to play it as an Intelligence caster, substitute any Charisma bonuses for Intelligence.

Additional Arcane Focuses 

Even if you are not a tome warlock, you can still use a book as your arcane focus. You can also use cards, a crystal ball, a staff, a gem, a scroll, a mirror, a wand, arcane glasses, or paper charms.

 

Expanded Spell List

1st level Arcane feature
Game Masters may change the available spells depending on your patron and what they choose to give. For example, if your patron is Mordenkainen, you may get Mordenkainen's Faithful Hound. With no specifics, here are the base spells.

Arcane Expanded Spells

Arcane Knowledge

Starting at 1st level, the magic of your patron's powerful influence grants you knowledge of the workings of the arcane. You gain proficiency in the Arcana skill and whenever you make an Intelligence (Arcana) or Intelligence (History) check, you gain a bonus to the check equal to your Charisma modifier (minimum of +1).

Additionally, you learn one cantrip of your choice from the wizard or sorcerer spell list. This counts as a Warlock spell for you and does not count against your spells known.

Teachings of the Arcane Master

Starting at 1st level, whenever you level up, you may swap a spell or cantrip out with a different spell. This effect is permanent until you level up again.

Additionally, you can attune to any magic item that is labeled for a wizard.

Magic Resistance

Starting at 6th level, your understanding of the arcane grants you resistance. You gain resistance to Force damage and, as a reaction to failing a saving throw caused by a spell, you can give yourself a bonus to that saving throw equal to your Charisma or Intelligence modifier. You can use this ability a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.

Additionally, you can use a spell scroll even if the spell is not on the Warlock spell list.

Assess Defenses

Starting at 10th level, you can bend magic to bolster the defenses of your allies or reduce your enemies. As an action, you use your arcane focus to direct the energy to a creature of your choice within 50 feet of you, allowing you to use your Charisma or Intelligence modifier to affect their AC. You can add your modifier to their AC, or subtract your modifier from their AC. There is no saving throw attached, but you must concentrate on this as if concentrating on a spell. You can concentrate on this additionally to a spell, but you must roll con saves if hit to maintain it. If left uninterrupted, this lasts for ten minutes. You can do this once per short rest. 

Master Arcanist

Starting at 14th level, your arcane mastery nearly rivals your patron's. The Slot Level of your warlock spells increases to 6th level rather than 5th level. You also learn one 6th-level spell of your choice from the sorcerer or wizard spell lists, which counts as a warlock spell for you, but don't count against the number of spells you know.

Additionally, Whenever you cast a warlock spell as an action, you can use a bonus action to cast a warlock cantrip that has a casting time of one action. You can cast a cantrip using this feature a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.