There’s a certain virtue in waiting. Sometimes, the wisest thing you can do is remain still — unmoved by hunger, boredom, or impatience — and wait for your moment. The most enlightened monks understand this.

By that logic, the Piercer might be the most enlightened creature in the Monster Manual.

Caves and caverns are a classic setting for D&D adventures, where a party can find Dwarven ruins, monstrous lairs, or portals to other planes. While exploring, they have to deal with the darkness, unexpected abyssal drops, narrow crevasses…. and Piercers. Strange, rock-solid monsters that cling to the cavern of the ceiling, still and unnoticeable, until something walks beneath them. Then it’s a quick drop, an impalement, and then the gnashing of teeth until the Piercer is fed.

An ambush predator like that is outstanding when it comes to creating that atmosphere of impending danger. The big combat that your players are looking for – fighting the dragon or wiping out the cave trolls – is great, but you can give the whole quest a greater sense of danger by hitting them when they’re on the way, dropping horrifying things from the shadows up above.

When you think about it, this is a really weird twist of evolution – a kind of biological min-maxing. It’s not smart, unbelievably slow, but if you need someone to drop onto your skull like a living stalactite and ruin your day, then this is your guy. And this really is its only trick; it walks at five feet per round, so if it misses, your party can just stroll away at a leisurely pace and not think about it again.

If your only plan is ‘fall real hard,’ you’d better make it count. And if one Piercer plummeting down on your players is fun, multiple Piercers, one after another, is downright funny. They should fall like hard, pointy rain on your players, perhaps driving them into hiding in a part of the caves that makes their final goal even harder to get to.

Piercers should teach your players to think three-dimensionally as well. If they’re used to looking at scenes from the top down, as you would on a tabletop battle map, they could get fairly complacent about where danger can come from. Hiding behind that rock, perhaps, or that bend in the tunnel. 2D maps are great at many things, but cueing in your players to danger from up above is not one of them.

You could even team up the Piercer with other creatures that like to hide high up in the darkness – your Cloakers and Darkmantles, Stirges and various oozes…. If you plan it right, your players are going to start fearing the heights more than anything else you’ve put at the end of their quest.

Now, to be fair, just randomly dropping stuff on your players without warning isn’t technically fun.

Well, it is, but maybe not for them.

So how do you telegraph to them that there are things in the high darkness that they need to worry about? Skeletons in the cavern with giant holes in the skulls? Discarded, dented helmets? Crunching noises from up above that your players with the best passive perception can hear? Perhaps there is a hastily-scrawled sign at the entrance to the caves that simply reads, “NEVER LOOK UP.”

Leaving clues and hints as to the true dangers of the underground may give your players a better chance for survival, but it could also utterly terrify them on the way.

While its attacks are singular, there is one very interesting thing about the Piercer – unique among the denizens of the Monster Manual, I think – is that they are explicitly the larval form of another, more terrifying monster – the Roper. The Manual states that Piercers move as quickly as they can (which again, isn’t very quick) away from their Roper parent so as to avoid being devoured. This means that the Piercer could foreshadow a Roper later on, provided your players are properly attuned to the natural world. If the Piercer is the egg, then the Roper is the scream that follows.

In fact, here’s a good NPC for you: the Cave Druid. This is the Druid who’s been living underground for years. They know everything about the creatures and the resources that can be found in the deepest darkness, and would be more than willing to guide your party through the caves. For a price.

Your players might even find themselves part of that ecology. Let’s say your party just killed a Roper. While exploring its lair, they come across a clutch of leathery eggs. And from one of those eggs… a tiny, sticky, one-eyed conical creature emerges. Now, as far as Party Pets go, it might not be as immediately adoptable as a baby Griffin or Displacer Beast, if you play it right, they might have the weirdest pet ever.

It would be even funnier if it somehow imprints on a Player and – again, very slowly – follows them through the cavern, looking for its new, less carnivorous parent.

Ultimately, Piercers aren’t the cutest, the strongest, or the fastest monsters in the game. They don’t carry loot, they don’t make speeches, and they’re never going to destabilize a kingdom or conquer the world.

But if you want to make your players afraid of gravity itself?

Then they’re perfect.