Sometimes players are sloppy when it comes to exploration. They rush around the map as though they are in a perfectly safe place, nary a Perception check in sight. There are of course, more than a few ways to help them learn to be a little more cautious. The cloaker, with its Damage Transfer ability, is probably one of the most elegant.
The cloaker is a cave dweller. It’s like a nasty flying manta ray with a proclivity for attaching itself to people’s heads. That’s just what it does if it lands an attack with advantage, but it’ll still give your players a nice hug even without advantage. Then the Damage Transfer trait kicks in:
Damage Transfer While attached to a creature, the cloaker takes only half the damage dealt to it (rounded down). and that creature takes the other half.Monster Manual, p. 41
Suddenly this combat encounter has gotten a bit more complicated! The cloaker also blinds and suffocates if it attaches to the head. We’ve gone from an ordinary combat encounter to a race to save the life of a comrade being slowly smothered by a monster you’d rather not hit. Cloakers make for a great encounter on their own, but really spice up more complex encounters as well. Next time your wizard friend immolates some duergar with a fireball, maybe the cloaker hiding among the stalactites is disturbed?
Monsters with Damage Transfer:
Rugs of smother work in a similar way, although they use grapple and restraint, limiting the target of their attacks even further. Before it’s reprint in Mordenkainen Presents: Monsters of the Multiverse, slithering tracker had the same trait as well. While the MPMM version no longer has the trait, it does have the same text in the attack that triggers its grapple. The publishers of Dungeons and Dragons are in the process of simplifying monster stat blocks for ease of use; Removing traits and consoldating the text from them into the attack is part of the way they are doing that.
After you take a look at cloakers, if you’re looking for something else nasty to throw at your players, I’ve got a lot of monsters on my Hotlist. Absolutely every single one of them is a blast in a combat encounter.