Let's talk about a weird one today. Flail snail first appeared in the Fiend Folio in 1981. They didn't see any use in the 1e system after that, at least not in official modules. In fact, it only shows up in 12 total adventures from TSR. Two of them were in Dungeon Magazine.
The flail snail has always been one of my "guilty pleasure" monsters. Let's go through the checklist:
Easily recognizable - yes
Unique abilities - yes
Multiple attacks - yes
Dungeon dweller - yes
Messes with magic - yup
They are in the "sweet spot" for adventuring too. 4-6 HD is perfect for the E/X (levels 3-9) play. And they circumvent standard party tactics. Immune to fire and poison, it also can rebound spells. Fighting types don't want to get close because they have a high number of attacks. AND . . . When they die, they wail for 1-3 turns, adding a 50% penalty to wandering monster checks.
That's a pretty fun package, when all rolled together. But, they are WEIRD. How do you use such a creature?
Egg, the great wizard of Mord Mar loved having flail snails in and around his tower. Their scintillating shells and relative obscurity thwarted several theft attempts in his tower.
The hobgoblin, Mucksnort, recently led an expedition to capture a flail snail. Much to his delight, they captured two, and a clutch of eggs. Now he leads his hobgoblin military from the back of his new mount, and his lieutenant keeps the female with her eggs at their swamp abode.
The great zoo in Redstone recently got in two specimens of flail snail. However, the staff had no idea how to contain or control them, and now they are leaving slime trails throughout the city. They batter down walls at dawn, so they are easy to track down, but they need to be reclaimed alive.