I love these for sneak attacks in dungeons for starting adventurers. New adventurers may be searching the ground for traps and such in a cave but don't usually expect a stalactite to come alive and attach to their heads. Good fun! Using their Darkness can actually lure unsuspecting folks close, thinking perhaps there is something of value hidden within.

It has basically become an inside joke anytime my Paladin PC enters a cave or the Underdark, he is almost guaranteed to get attacked by one of these things.

So just to clarify, a Drow's Superior Dark Vision and/or a Warlock w/ Devil's Sight can see perfectly fine with in the darkness Aura?

yes, I think

Quote from Anthos1682 >>

So just to clarify, a Drow's Superior Dark Vision and/or a Warlock w/ Devil's Sight can see perfectly fine with in the darkness Aura?

Yes, Devil’s Sight will go right through that magical darkness.

Drow, However, will require some assistance from a skill or special feature.

Can a glowing sword ‘cut’ though the darkness?

(See what I did there)

The DM for my main group is thinking about letting my Shadow Sorcerer keep one of these fellas as a pet. 

Flying squid😟

Quote from Synthania_Sylverleaf >>

Can a glowing sword ‘cut’ though the darkness?

(See what I did there)

 Assuming it’s fairly powerful item:  yes.

"While attached to the target... The Darkmantles speed also becomes 0." Yet, "On its turn, the darkmantle can detach itself from the target by using 5 feet of movement."

Question:  How can the Darkmantle use 5 of its feet of movement to detach itself, if its speed has become 0?

I think the idea is that as soon as it detaches, its speed returns to its standard amount, minus 5 feet from the detachment action.

Cool, that's what I imagined, but wanted to make sure. Thanks :)

THESE THINGS CAN FLY?!

Quote from Adran_Galanodel >>

THESE THINGS CAN FLY?!

They're also great at hanging from shadowed ceilings & then "falling, with style". 

I just realized these are like the perfect seeing-eye-dog for a blind old cloaker.

If the targeted creatures can't breath, most party members will be surprised by the attack and otherwise unable to hold their breath, resulting in the rules for suffocation to kick in. Even for higher level characters, unless you walk around with a piercing weapon pointed to the ceiling (or you don't need to breathe), these creatures will likely spell a quick doom to anyone attacked (anyone attacked is blinded, anyone within 15 feet is blinded due to the darkness ability of the creatures, although not necessarily stated, you would think that any targeted creature is likely restrained, and unless you are instantly ready to suck in a deep breath and hold it whenever darkness suddenly overcomes you, you're going to suffocate in a matter of rounds!

I'm so looking to throwing a few of these at my party and see what happens. 

Suffocating Rule

A creature can hold its breath for a number of minutes equal to 1 + its Constitution modifier (minimum of 30 seconds).

When a creature runs out of breath or is choking, it can survive for a number of rounds equal to its Constitution modifier (minimum of 1 round). At the start of its next turn, it drops to 0 hit points and is dying, and it can't regain hit points or be stabilized until it can breathe again. (if you are not prepared to hold your breath, this would be the default condition for most PCs)

For example, a creature with a Constitution of 14 can hold its breath for 3 minutes. If it starts suffocating, it has 2 rounds to reach air before it drops to 0 hit points.

EDIT: I reread the stat block and noticed something I missed previously (about the target of a darkmantle's attack having the ability to detach the creature by making a successful DC13 strength check as an action.) You can still brought to 0 HP in short order, but if you have a decent athletics skill or a higher constitution, you either have a better chance of removing the thing or surviving long enough to get a few chances at tearing it off from you!

******* legend

I just had a group of three of these TPK a level 2 party of 4 adventurers. An interesting concept was brought up that I figured I'd share.

One of them asked if they could attack the one on their head. I agreed, but as per the blinded condition, they'd have disadvantage. They argued that they KNEW where the creature was and that the disadvantage shouldn't be applied. In the end, I gave them a choice. If they wanted to attack the part of the darkmantle wrapped around their face and throat, they can make a regular attack, but as they can not see exactly how the creature lies upon them, they would also deal half their damage to themselves. Alternatively, they could attack the upper part that is resting on their head at disadvantage due to the blindness and awkward strike angle but if they hit, only the monster would take damage.

Another player asked if he could just ram his head into the wall. I agreed and treated it as an unarmed strike.

In the end, they managed to kill 2 of the monsters, but when it was down to one remaining darkmantle vs one party member at 1 hp...well it didn't go well for them.

Hmm, no damage transfer when attacking a 'mantle that has engulfed a target?

I wonder how much I'd need to bump the CR by if I included that ability? :\

Sounds like you made the encounter harder then it needed to be, if it was on their head they would've easily been able to swing at the creature without disadvantage even without harming themselves depending on the weapon. They're level 2 take it easy on em lmao

what could adventurers ponentoaly get if they seach it and cut it apart for snacks