"You have made a pact with a fiend from the lower planes of existence, a being whose aims are evil, even if you strive against those aims. Such beings desire the corruption or destruction of all things, ultimately including you. Fiends powerful enough to forge a pact include demon lords such as Demogorgon, Orcus, Fraz’Urb-luu, and Baphomet; archdevils such as Asmodeus, Dispater, Mephistopheles, and Belial; pit fiends and balors that are especially mighty; and ultroloths and other lords of the yugoloths."

The traditional Fiend subclass is too generic for you. You take your powers from the Lord of No Mercy himself, Mephistopheles, and you want everybody at your gaming table to know it. You either have a direct pact with the archdevil, or with one of his many followers (example: Hutijin) who channels the powers to you. Whether your ideals are in line with the archdevil's evil machinations or not is up to you, but your actions are unmistakably born from the same fiery fury that makes the enemies of the Cold Lord tremble with fear. Embrace the dark powers within you, unleash your inner devil, and watch the world around you burn in your wake.

Expanded Spell List

The Fiend (Mephistopheles) 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.

Fiend Expanded Spells

Spell Level	Spells
1st	burning hands, detect magic
2nd	blindness/deafness, flame blade
3rd	fear, fireball
4th	arcane eye, fire shield
5th	hallow, immolation

Mephistopheles' Fury

Starting at 1st level you learn the fire bolt cantrip. It counts as a warlock cantrip for you but does not count against your number of cantrips known.

Additionally, you have access to new eldritch invocations specific to your patron, detailed below. You still need to fill the prerequisites to learn the invocations.

Lingering Bolt

Prerequisite: fire bolt cantrip

When you deal damage to a creature with fire bolt, that creature must succeed a Dexterity saving throw against your spell save DC or catch on fire. Once on fire, the creature takes fire damage equal to your Charisma modifier (minimum of 1) at the start of each of its turns until it uses its action to put out the flames.

Immolating Bolt

Prerequisite: 5th level, fire bolt cantrip

When you cast fire bolt, add your Charisma modifier to the damage it deals on a hit. Additionally, your fire bolt cantrip ignores fire resistance and treats creatures that are immune to fire damage as if they only had resistance to fire damage.

Inescapable Blaze

Prerequisite: 7th level, fire bolt cantrip

When you cast fire bolt, its range is 300 feet and your ranged spell attack ignores half cover and three-quarters cover.

Frost of Cania

Prerequisite: 9th level

You gain resistance to cold damage. Whenever you cast a spell that deals cold damage, you gain a +2 bonus to the damage roll.

Archdevil's Immortality

Prerequisite: 12th level

If you somehow have multiple sources of resistance to the same damage type, you instead gain immunity to those damage types. Additionally, you stop aging and can no longer die from old age.

Arcane Might of the Merciless Lord

Prerequisite: 15th level

You can cast counterspell at will, without expending a spell slot or material components. Once you've successfully countered a spell of 4th level or higher using this feature, you must finish a long rest before you may use it again.

Mephistopheles' Right Hand

Prerequisite: 18th level

As an action, you can summon the archdevil Hutijin to an unoccupied space within 30 feet of you. Hutijin hates being summoned and will treat anybody within visual range as a hostile enemy that must be slain with extreme prejudice except for you and your allies, who he regards with indifference because of your allegiance to Mephistopheles. If however there are no other enemies in sight the illusion of indifference is broken and he treats you and your allies as hostile. He acts on his own initiative and does not obey any commands. Hutijin remains on your plane for a number of rounds equal to your Charisma modifier + 1 (minimum of 1) before returning to Cania.

Once you've used this feature you cannot do so again for 10 days.

Dark One's Spell Shield

Starting at 1st level, you can call on the arcane prowess of Mephistopheles' to shield you against certain spell attacks. As a reaction when making a saving throw against a spell you can see being cast, you can give yourself advantage on that saving throw. If you succeed on the saving throw after giving yourself advantage, you gain temporary hit points equal to the spell’s level + your Warlock level + Charisma modifier (minimum of 1; treat Cantrips as level 0).

Dark One’s Spell Leech

Starting at 6th level, you can siphon the arcane reserves of your allies. As a bonus action, choose one ally you can see within 30 feet. The target loses its lowest-level available spell slot, and you gain it.

Once you use this feature, you can’t use it again until you finish a short or long rest.

Fiendish Resilience

Starting at 10th level, you can choose one damage type when you finish a short or long rest. You gain resistance to that damage type until you choose a different one with this feature. Damage from magical weapons or silver weapons ignores this resistance.

Hurl Through Cania

Starting at 14th level, when you hit a creature with an attack, you can use this feature to instantly transport the target to Cania, the home plane of Mephistopheles. The creature disappears from its space and is hurtled through the frozen, nightmarish landscape of the 8th layer of Hell.

At the end of your next turn, the target returns to the space it previously occupied, or the nearest unoccupied space. If the target is not a fiend, it takes 8d6 cold damage and 8d6 psychic damage as it reels from its horrific experience.

Once you use this feature, you can’t use it again until you finish a long rest.