D&D 5e: Fathomless Warlock Guide

D&D 5e: Fathomless Warlock Guide

Role in the Party

The Fathomless Warlock is similar to the Great Old One in that they both involve a lot of tentacles; however, the tentacles of the Fathomless come from the depths of the ocean rather than the depths of space. Regardless, you could probably flavor the Fathomless features to work with a space or far realm-based patron.

While there’s not much discussion around the Fathomless Warlock, it’s still a decent choice for a warlock character who plans on having most of their levels be in warlock. Your features center around dealing damage to enemies while restricting their movement, and you have some water-based utility.





Fathomless Warlock Features

Expanded Spell List

The Fathomless 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.

1st: Create or Destroy Water is extremely circumstantial unless you’re in a desert campaign, but Thunderwave is a solid low-level option. Switch it out at higher levels; you only have pact slots and upcasting Thunderwave is not a great idea.

2nd: Gust of Wind is a somewhat underwhelming movement controlling spell, but Silence is a solid area denial option to use on enemy spellcasters, and it’s especially good if you can get the enemies stuck in the area somehow.

3rd: Lightning Bolt isn’t as good as Fireball, but sometimes you just need to zap a lot of enemies. Sleet Storm is a pretty good crowd control effect.

4th: Control Water is powerful and versatile but only if there’s a lot of water nearby, and  Summon Elemental is a powerful Tasha’s summon spell.

5th: Bigby’s Hand is a great spell, and having it appear as a tentacle is fun. Cone of Cold is probably a worse option than Synaptic Static, which you can already take.

Tentacle of the Deeps

At 1st level, you can magically summon a spectral tentacle that strikes at your foes. As a bonus action, you create a 10-foot-long tentacle at a point you can see within 60 feet of you. The tentacle lasts for 1 minute or until you use this feature to create another tentacle.

When you create the tentacle, you can make a melee spell attack against one creature within 10 feet of it. On a hit, the target takes 1d8 cold damage, and its speed is reduced by 10 feet until the start of your next turn. When you reach 10th level in this class, the damage increases to 2d8.

As a bonus action on your turn, you can move the tentacle up to 30 feet and repeat the attack.

You can summon the tentacle a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.

This is a solid built-in damage option that might not deal a ton of damage, but it also comes with a slowing effect. Combine this with the Lance of Lethargy invocation and maybe some difficult terrain or another movement-restricting spell to lock down your enemies effectively.  It does cost a bonus action every round though, so it’s incompatible with Hex, the Telekinetic feat, and a lot of other solid bonus actions. Still a good feature.

Gift of the Sea

Also at 1st level, you gain a swimming speed of 40 feet, and you can breathe underwater.

This is a great feature if you’re in a campaign with a lot of water, but otherwise, it’s just a nice ribbon feature to have. You’re faster in the water than on land, so jump in the water if you need to go faster.

Oceanic Soul

At 6th level, you are now even more at home in the depths. You gain resistance to cold damage. In addition, when you are fully submerged, any creature that is also fully submerged can understand your speech, and you can understand theirs.

Cold damage resistance is nice, and the communication aspect is circumstantial but hilarious. If you encounter a strange tribe in the jungle that you don’t share a language with and nobody has Comprehend Languages, and you think you can get away with it, drag one of their people into the river so you can talk to them. Make your conversation quick if they can’t also breathe underwater, because even though you can understand drowning people as written, they can’t communicate with you if they’re dead.

Guardian Coil

At 6th level, your Tentacle of the Deeps can defend you and others, interposing itself between them and harm. When you or a creature you can see takes damage while within 10 feet of the tentacle, you can use your reaction to choose one of those creatures and reduce the damage to that creature by 1d8. When you reach 10th level in this class, the damage reduced by the tentacle increases to 2d8.

This doesn’t prevent a ton of damage, but it works against any damaging effect, attack or not, and it’s only limited by your Tentacle of the Deeps total number of uses. Remember that this conflicts with reactions like Absorb Elements and Shield, so if you multiclassed for those, there is some conflict.

Grasping Tentacles

Starting at 10th level, you learn the spell Evard’s Black Tentacles. It counts as a warlock spell for you, but it doesn’t count against the number of spells you know. You can also cast it once without using a spell slot, and you regain the ability to do so when you finish a long rest.

Whenever you cast this spell, your patron’s magic bolsters you, granting you a number of temporary hit points equal to your warlock level. Moreover, damage can’t break your concentration on this spell.

Evard’s Black Tentacles is a nice spell, and you are the best at casting it. Not only do you get 10-20 temporary hit points whenever you cast it, making it almost on par with an upcast Armor of Agathys for temporary hit points, but your concentration is also nearly unbreakable. Dispel Magic or a few monster abilities can end the spell, and some rare situations can force you to make a concentration save, but in 99% of fights, you’ll be fine. Also, you get a free casting every day and can use your existing pact slots to cast it.

Fathomless Plunge

When you reach 14th level, you can magically open temporary conduits to watery destinations. As an action, you can teleport yourself and up to five other willing creatures that you can see within 30 feet of you. Amid a whirl of tentacles, you all vanish and then reappear up to 1 mile away in a body of water you’ve seen (pond size or larger) or within 30 feet of it, each of you appearing in an unoccupied space within 30 feet of the others.

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

This is an emergency “get out of danger” teleport that has some problems: it’s unclear if an unconscious ally can be “willing”, and also, there has to be a pond-sized body of water within a mile of you that you’ve seen. There usually aren’t swimming pools half a mile away from the lich’s lair, and you can forget about ever finding a pool of water in the Plane of Fire. This is excellent in a nautical campaign, but it’s your only 14th level feature, so it’s not even like earlier features that are water-based but come alongside a more broadly applicable feature. This does have a small chance of saving you from a TPK, but it’s unreliable, so it’s a bit meh.



You’re one of the best warlock options in a nautical campaign, and your features will restrict enemy movement, so you pair excellently with ranged party members and when fighting melee enemies. Your expanded spell list is solid, and you can deal decent damage.


Nothing in this subclass boosts your defense except for the usual defensive benefits of slowing distant enemies. A slowed archer enemy or spellcaster might not even care that their movement speed was reduced, and they can shoot whoever is far enough away from your tentacle to keep you from using your reaction to reduce the damage. Lastly, your water-based features are much less useful when there’s not any water around to use them with, and you’re not stellar in terms of raw damage.

Best Race Options

Although an aquatic race might seem thematic, remember that you get a 40-foot swim speed and water breathing at level 1. It’s probably best to pick a race that doesn’t have redundancy with this.

The Tabaxi’s Feline Agility works with your swim speed: double your speed to 80, take the dash action, and you can move 160 feet on your turn if necessary. The free Perception and Stealth proficiency are also nice, and Darkvision is handy for seeing in the depths.

If you pick a flying race such as the Fairy, you can be a master of land, air, and sea. The free low level spells are also a handy supplement to your Pact Magic.

Rules as written, the Bugbear’s Long-Limbed feature applies to the tentacle since the wording says that you make the melee spell attack and not the tentacle. This probably wasn’t intended, but it is funny, and it’s a solid race overall.

Choosing the Right Skills

As a warlock, allies will look to you for social skills like PersuasionDeception, and occasionally IntimidationPerformance is much rarer, so there is no need to specialize in it unless you want to.

Every character wants Perception proficiency since it’s the most used skill in the game, so make sure to grab it.

Make sure to grab Acrobatics proficiency in case you need to do something physical or escape a grapple; you can become as slippery as your tentacles.

ArcanaReligion, and Nature proficiencies all make sense for a warlock who worships the spooky creatures of the deep, so pick your favorites, or Arcana if you’re unsure which one is best.

Fitting Feats

There’s an invocation that gives you advantage on concentration saving throws, and you’re probably not using a weapon, so War Caster is not your best choice. Resilient (Constitution) is still very solid if you really want to boost your constitution saving throws.

Mobile is unusually useful on you compared to most warlocks; your Tentacle of the Deeps is a melee attack, and you are making it, so it lets you freely walk away from enemies without disengaging. You can then use your action to cast a spell like Eldritch blast, possibly slowing and pushing the enemy enough to make them unable to reach you. This also increases your swimming speed to 50 feet.

Sometimes you want to use Misty Step to escape a Wall of Force or another effect, but upcasting Misty Step with a 5th level pact slot hurts. Fey Touched has you covered, since it will give you a free use of Misty Step and one other spell, and it will boost your charisma score. 

Optimal Backgrounds

For a nautical campaign, Shipwright is a solid background. Your “I’ll patch it!” feature lets you give your ship some healing, but it’s ambiguous as to how long it will take.

Perhaps you’re an Archaeologist who searches for lost shipwrecks and ancient aquatic lore instead of digging through the dirt; if you’re in a land-based campaign, maybe you found a good lead for a treasure on land using clues you discovered in the sea. Work with your dungeon master if this sounds like a good idea to you

Nobody can escape the almighty Strixhaven Backgrounds; pick your favorite. I would recommend grabbing Find Familiar from a wizard spell list option over Shield unless you’re doing a multiclass that gives you 1st level spell slots and no Shield (such as into Bard) since Shield is less useful if you don’t have low level slots to fuel it with.

Multiclassing Options

One level of Divine Soul Sorcerer will grant you Shield, Absorb Elements, some slots to fuel them with, and a 2d4 you can add to an attack or saving throw once per rest. Starting as a sorcerer also gives you constitution saving throw proficiency. Solid multiclass. Take two more levels if you want Metamagic and more spell slots, but that will delay higher level Warlock slots and your Mystic Arcanums.

One level of Twilight Cleric will drastically boost your initiative and give you utterly ridiculous darkvision that lets you see in the ocean depths for 300 feet in all directions, plus proficiency in all armor and a few other benefits. Peace is stronger, but it’s annoying to remind your whole party to use their d4 or that they already used their d4 that turn, so I would recommend Twilight more.

If you’re high level, looking for some multiclass options, and have the intelligence for it, why not grab two levels of Wizard for Find Familiar, some other useful spells, and the Divination subclass? Portent is fun.

Would I recommend playing a Fathomless Warlock?

I completely recommend the Fathomless Warlock in a nautical campaign, and I recommend it somewhat more weakly for a land-based campaign. You can still be an effective character even on land, but it’s more fun if you get to use that swimming speed and that high level teleport option.

I also don’t recommend the Fathomless Warlock as a 1-3 level dip as much as the classic Hexblade, Undead, and Genie: other characters just don’t get as much by dipping Fathomless unless they’re in a nautical campaign and want an easy swimming speed. It’s not an awful choice, but there are significantly better picks.

Sage Gamers

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