It seems a universal rule that from comics to boardgames, all aspects of nerd culture must eventually make some sort of nod to the Cthulhu mythos. In D&D this often manifests in the form of Warlocks battering people with otherworldly tentacles.
There are actually a worrying number of spells that allow you to do this, but the simplest is Arms of Hadar. It’s first-level spell that’s exclusive to the Warlock list and summons “tendrils of dark energy” that attack every creature within 10ft. of you.
For anyone curious, those tendrils are probably being supplied from Beta Centuri, a star system is the Centaurus constellation that is also known as Hadar. Quite how this happens isn’t exactly clear, but that’s what magic is for.
Etymological discussions aside, the spell’s damage is a little on the low side – only 2d6 – and it’s necrotic so is resisted by an annoyingly large number of foes. However, the area it can effect is pretty impressive for a first-level ability and any creature that fails it save is too busy fending off tentacles to make reactions until its next turn, hopefully leaving the Warlock free to slip away without taking opportunity attacks.
The nature of Warlock spell slots means that for the vast majority of the game you’ll be casting it at higher levels. Again, the scaling is a little anemic, dealing only 6d6 when fired off through a fifth-level slot.For comparison, this is just over half of the damage a Fireball using the same slot would cause, with a smaller area of effect and the requirement that you’re standing right in the middle of the enemy formation.
It’s a wonderfully evocative spell that is great RP-bait for Great Old One pact Warlocks and can be a useful spell for a Warlock who wants to get out of a pickle, but it’s also very situational.
The fact that Arms of Hadar hits everyone in range, no matter of their allegiance, severely restricts its ability to counter an ambush or charging enemies, and ideally traditional long-range spellcasters should never get into a situation when they’re surrounded by enemies in the first place. Even Blade-locks probably have better uses for their spell slots once they get a few levels under their belt.
If you’re desperate for a chance to use tentacle-based attacks – which is entirely understandable – it might make sense to keep it on hand until you can learn the much more effective (and thoroughly creepy) Hunger of Hadar and then swap it out for something more practical.
At first level Arms of Hadar is a decent spell for getting you out of sticky situations and dealing damage over a wide area. However, despite its awesome flavour it soon gets outclassed and is probably best left by the wayside.
Arms of Hadar
Casting Time: 1 action
Range: Self (10-foot radius)
Components: V, S
You invoke the power of Hadar, the Dark Hunger. Tendrils of dark energy erupt from you and batter all creatures within 10 feet of you. Each creature in that area must make a Strength saving throw. On a failed save, a target takes 2d6 necrotic damage and can’t take reactions until its next turn. On a successful save, the creature takes half damage, but suffers no other effect.
At Higher Levels: When you cast this spell using a spell slot of 2nd level or higher, the damage increases by 1d6 for each slot level above 1st.