Guide to Building a Warlock Fathomless Patron: DnD 5e

Warlocks who use The Fathomless as their patron benefit from an expanded list of water-based spells and the aid of spectral tentacles.  This patron comes from the Elemental Plane of Water—an unknown being of the abyss.  Of course, tentacles are kind of a big deal to this warlock, which works well as a Lovecraftian theme.  A warlock who follows the Fathomless has an air of adventure about them—great for pirate or coastal campaigns.

When building a warlock of the Fathomless Patron in DnD 5e, consider:

• A race with strong Charisma and spellcasting
• Choose Pact of the Talisman
• Choose warlock spells with lightning and tentacles
• Eldritch Invocations: Rebuke of the Talisman, Misty Visions
• Fathomless abilities: Tentacle of the Deeps, Gift of the Sea…

Before we dive in, check out my original pirate adventure when playing your fathomless warlock.  Click here or below to learn more.

A race with strong Charisma and spellcasting

One of my favorite contenders for this class is the triton.  Obviously, these water-dwelling merfolk(ish) people fit the theme well.  Plus, they get a +1 bonus in Charisma, Strength and Constitution and their own set of sea-based spells.  Fog cloud and wall of water can add further field effects in combat, leaning into my spooky command over the ocean.

Fallen aasimar can also make an interesting warlock of the deep, leaning on a +2 Charisma/+1 Strength bonus.  This fallen angel could connect with a new Lovecraftian creature of the Elemental Plane of Water, changing loyalties from a celestial master.  Plus, they can cast a Necrotic Shroud, which sprouts skeletal wings from their backs and makes enemies afraid.  I can also deal extra necrotic damage with a weapon attack equal to my level.

Choose Pact of the Talisman

As I begin my path down the warlock class, I’ll start my character with an arcane focus and a dungeoneer’s pack.  I figure the adventurous aspect of this built needs as much.  I’ll also choose Deception and Nature as proficient skills.  The Deception check plays off my high Charisma score, and the Nature check connects with my sea theme.

Introduced in Tasha’s Cauldron of Everything, Pact of the Talisman adds 1d4 to failed ability checks.  As opposed to the high aggression of the Pact of the Blade or upkeep of the Pact of the Tome, this feels more accommodating to adventurers.  As I level, I can choose Eldritch Invocations for further enhancements with this pact.

Choose warlock spells with lightning and tentacles

Warlocks learn fewer spells than some of their magical counterparts.  However, these spells are effective and boosted with Eldritch Invocations.  For this build, I want to lean on spells that have a tempest flavor—stuff related to weather—as well as ocean-themed creepiness from the abyss. I would suggest dabbling in summoning magic with Tasha’s Cauldron of Everything—especially summon shadowspawn.

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Cantrips

• Eldritch Blast: crackling energy deals 1d10 force damage. This cantrip is for basic ranged attacks—a classic of the warlock class.
• Lightning Lure: Foe must make a Strength saving throw or be pulled 10 feet toward me. If they come within 5 feet of me, they receive 1d8 lightning damage.  I’m thinking this could have fun tentacle visuals and also set up my tank for a smack down.
• Mage Hand: I can reach out with an ethereal hand and manipulate items from 30 feet away. Of course, my ethereal hand might look more like a tentacle.  This cantrip is one of my favorites—carrying so many creative uses.

1^st-level spells

• Arms of Hadar: I evoke the wrath of Hadar, the Dark Hunger. Dark tendrils shoot from my hands, forcing targets within 10 feet of me to take Strength saving throws.  On a failed save, they take 2d6 necrotic damage and can’t take reactions until their next turn.
• Expeditious Retreat: I can take the Dash action when I cast this spell and each turn after as a bonus action.
• Hex: Place a curse on a target and deal extra 1d6 necrotic damage when I hit it with an attack. Plus, I can choose an ability and give the target disadvantage on rolls using that ability.
• Witch Bolt: Send crackling lightning toward a target for 1d12 lightning damage. For 1 minute, I can use my action to deal 1d12 lightning damage without expending a spell slot.

2^nd-level spells

• Invisibility: Magically turn invisible.  This spell ends if I attack or cast another spell.
• Misty Step: Teleport up to 30 feet away in a wisp of vapor. This spell is the king of escaping hairy situations.

Fathomless Extended Spells

The Fathomless patron’s extended spell list gives me options for storm and sea magic.  These options range from 1^st-level spells to 5^th-level spells.

Level 1

• Create or Destroy Water: You guessed it, I can create or destroy 10 gallons of water.  Options include extinguishing fires and dissipating fogs, along with, you know, basic survival needs.
• Thunderwave: Within a 15-foot cube, creatures must make a Strength saving throw or be pushed 10 feet away with 2d8 thunder damage.

Level 2

• Gust of Wind: Create a massive gust of wind that pushes creatures 15 feet away on failed Strength saving throws.
• Silence: A 20-foot-radius sphere of silence is created within range. No verbal components for spells can be used here, nor can anyone take thunder damage.  Also, creatures are deafened while inside.

Level 3

• Lightning Bolt: a 100-foot-long line of lightning strikes blasts every creature in its path, dealing 8d6 lightning damage. Creatures in range must make a Dexterity save, taking half as much damage on a successful save.
• Sleet Storm: A 20-foot-tall cylinder with a 40-foot radius blasts the ground and air with sleet. The area turns icy, making it difficult terrain.  When a creature enters the field, it must make a Dexterity save or fall prone.

Level 4

• Control Water: I can flood an area with water, part seas Moses-style, create whirlpools and redirect water flow.
• Summon Water Elemental: This elemental can be found in Tasha’s Cauldron of Everything, using the elemental block and choosing the “water” variant.  Plus, it comes with 50 HP, 30 feet of swim speed, the ability to move through inch-wide openings, a multi-attack and mean slam for 1d8 + 8.

Level 5

• Bigby’s Hand (tentacle version): I can summon a tentacle that follows the direction of my hand. This tentacle has an AC of 20 and as many hit points as me.  I can make attack, push, grapple and deflect with this tentacle: Clenched Fist, Forceful Hand, Grasping Hand and Interposing Hand.
• Cone of Cold: blast a 60-foot cone of 8d8 cold damage. Creatures in the area must make a Constitution saving throw.

Eldritch Invocations: Rebuke of the Talisman, Misty Visions

Eldritch Invocations are special abilities and spell effects offered to the warlock class.  Even if the warlock doesn’t learn as many spells as the wizard, these Invocations more than make up for it.

Rebuke of the Talisman offers me a defensive ability for when enemies close in, dealing a small amount of damage and pushing them back 10 feet.  The damage dealt is equal to my proficiency modifier, so I’m mostly counting on the push and pull aspects this character offers in battle.  Of course, I’ll need to have the Pact of the Talisman to use this ability.

Misty Visions gives me the ability to cast silent image on command.  No spell slot needed.  A 1^st-level spell, silent image is able to create monsters, people and objects that aren’t really there.  I like the aspect of illusion magic connected with the sea theme.  Especially as a warlock, this ability can come in handy for trickery, fear and confusion.

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Fathomless abilities: Tentacle of the Deeps, Gift of the Sea…

The Fathomless patron offers this warlock the ability to survive in deep sea environments, as well as summon a spectral tentacle to attack and defend.

Tentacle of the Deeps summons a 10-foot spectral tentacle at any point I can see within 60 feet.  This creation lasts 1 minute or when I summon it somewhere else.  I can make an attack for 1d8 cold damage, reducing the enemy’s speed by 10 feet.  Plus, as a bonus action, I can move this tentacle 30 feet.  I can summon this weapon an amount of times equal to my proficiency bonus.

Gift of the Sea is another level-1 ability for the Fathomless, giving me a swimming speed of 40 feet.  I can also breathe underwater.

Oceanic Soul is learned at level 6, granting me resistance to cold damage and giving me the ability to communicate with undersea life.  However, I’ll have to be submerged with the creature.

Guardian Coil offers new tricks with Tentacle of the Deeps, causing my reaction to reduce damage to an ally.  Anyone I choose within 10 feet of me reduces attack damage by 1d8.  It’s kind of like a whipping defensive maneuver.  This ability is also learned at level 6.

Grasping Tentacles (level 10) grants me a special version of the Evard’s black tentacles spell.  With this spell, I create a 20-foot square of writhing tentacles, dealing 3d6 bludgeoning damage to those caught.  Creatures must make a Dexterity or Strength save or remain restrained.  I can cast this spell once a day for free and gives me temporary HP equal to my warlock level.

Finally, Fathomless Plunge gives me teleportation abilities, summoning a whirl of tentacles that transports me and up to 5 allies 1 mile away.  The portal connects me to a body of water I’ve seen within that mile.  Either my party appears in the water or 30 feet away on shore.

To Sum it Up

This warlock has pirate written all over him or her.  If I had to guess, I would say the class’s tentacle abilities were inspired by Bigby’s hand.  Tentacles are some of the creepiest aspects of the deep, and this class uses that fact to great effect.  The class overall seems like an updated Great Old One patron, leaning on the Cthulhu side of that lore, but wow are the upgrades and oceanic effects cool.