My Failed Flail Snail Trap

Last session, my players reached a room in my mega-dungeon that I had designed months ago. I’d been looking forward to seeing how they would tackle it, and their solution didn’t disappoint. Here's a breakdown of the room.

The Setup

The chamber is 60 feet long and 30 feet wide. At the far end stands a large, heavy door, secured by two chains that split off to separate winches and handles embedded in the floor. Near the entrance, there are two glass enclosures containing large snail shells, home to a pair of Flail Snails. The glass enclosures have sliding doors similar to the main exit.

To open the door and proceed through the dungeon, two party members must grab the handles and pull the chains southward. This requires two players to commit fully to the task, leaving them unable to contribute to combat. If they let go of the handles, the chains snap back, and the door slams shut, resetting their progress.

Here’s the catch: the winch mechanism also controls the glass doors of the Flail Snail enclosures. As the party opens the main door, they must also deal with an emerging threat.



How the Players Surprised Me

What I envisioned as a tense, drawn-out encounter turned into a brilliant example of player ingenuity. I expected them to avoid the room entirely and come back with more fighters, but they took an entirely different approach.

First, they cast sleep on one of the Flail Snails—a clever move to halve their opponents right away. Next, they opened the main door while forming a defensive line to hold off the remaining snail.

One player remembered my earlier description of the heavy glass doors and devised an ingenious plan: they let go of the winch, causing the door to slam down on the active snail. The impact dealt massive damage, pinning the creature in place. (Snails aren’t known for their evasiveness) From there, they quickly dispatched the trapped snail, spiked the handles to keep the main door open, and continued into the dungeon.

What I had intended as a challenging fight turned into a relatively easy encounter, thanks to the party using the trap against itself. As a DM, this was a proud moment. It’s always rewarding to see players outsmart a challenge, even if it didn’t go as planned. It also gave me a valuable opportunity to reflect on the room’s design.

What I Learned and How I'll Improve It


I still love the core concept: part of the group is preoccupied with a task while the rest must manage combat. But now, I’m thinking about how to refine the challenge to keep things engaging as the players grow more resourceful. Here are my ideas for improvements:

  1. Enchant the Glass Enclosures
    The glass doors could be enchanted to protect the snails from spells like sleep. This would force the players to engage with the snails more directly. To avoid frustrating them, I’d telegraph this enchantment subtly—perhaps with magical glyphs easily identifiable as anti-magic. 

  2. Trigger the Enclosures Automatically
    Instead of having the enclosures open gradually as the main door is raised, the snails could be released at a specific point in the task. This could even be hidden from the players, would just need to make sure there are other signposts, such as trails of slime on the floor and a few dead adventurers. 

My Updated Room Design

In the revised version, the room remains largely the same. The enclosures will also release the snails automatically when the main door reaches its halfway point, keeping the timing of the danger unpredictable. The enclosers will also be on the sides of the room, really splitting the party.


To hint at what’s to come, I’ll add subtle environmental clues, like slime trails leading to the enclosures and remnants of earlier victims. These details should help the players anticipate the danger without outright spoiling the surprise. This room is also on floor 3. By this point, they should have an idea of how I run things and what to look out for. I should stop being so kind to them!

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