Are there any creatures or monsters that heal from Necrotic damage?

Just what it says.  I don't mean resistant/immune, but actually are healed by incoming necrotic damage.

Thanks in advance!

Not by RAW. At least not in a WotC product. There could be a 3rd party thing out there that has that effect.

That used to be a thing in 3e, where necrotic would heal undead, but it no longer does.

Necrotic damage? No. But the Shambling Mound is healed by lightning. And the Clay Golem (i think) is healed by acid damage. 

Quote from AnzioFaro >>

Necrotic damage? No. But the Shambling Mound is healed by lightning. And the Clay Golem (i think) is healed by acid damage. 

Interestingly enough the mound is the answer to OP's question.

Undead Shambling Mound trades the lightning absorption of the Shambling Mound for necrotic absorption. It also adds the poison/poisoned immunities of undead.

Though adding on to your list, flesh golems are also healed by lightning damage.

Though, OP, if you're keen on a monster that heals from necrotic damage for an encounter I'd probably default to a simple homebrew. Like adding it to a vampire/succubus or getting a monster you like and topping them off with the surprise. I don't believe it'll change the CR of a monster when looking at the general case. And in the situation where you have a party that likes to use necrotic a lot odds are the first time they deal necrotic damage and you say "its wounds begin to close up" they probably won't use necrotic again. So can just average out the damage to see how much additional HP it'll have.

"Cruelest" use would probably be to have a death knight with minions and give them additional healing from necrotic damage plus immunity to fire so that he can use the hellfire orb as a second wind.

Quote from Xalthu >>

Not by RAW. At least not in a WotC product. There could be a 3rd party thing out there that has that effect.

That used to be a thing in 3e, where necrotic would heal undead, but it no longer does.

 To be technical, in 3rd Edition it was called Negative Energy, and it would heal undead at the same rate it harmed living creatures, but at the same time Positive Energy spells that provided healing would damage undead.  Presumably it was changed so that PCs who wanted to focus on necromancy weren't so helpless against undead (or constructs, who were immune to most Negative Energy effects due to being nonliving).

Thanks!  Much appreciated.