Wandering Monsters: Gotcha!

There are a lot of reasons that I do not use a monster. Sometimes it is a simple matter of my campaigns not lasting long enough to see the characters reach a level where they can reasonably encounter it, whether that means not be instantaneously annihilated by a stray attack or defeat it. Sometimes it is just not what I want or need for the campaign I have in mind. Sometimes I look it over, read the flavor text, and it just fails to grab me.

Sometimes, it is just really, really cheap and stupid.

One of the reasons I hated traps in 3rd Edition was that they were often difficult, if not outright impossible to find. If you failed to spot one and triggered it, it would just attack you/force a save, and...that was it. Take damage, move on. In my experience new players will start out exploring a dungeon, find a trap, then resort to methodically inspecting any related surface or object afterwards, sometimes coming up with ridiculous methods to bypass a trap that might not even be there, or convincing someone else to go first "just in case".

Often this would just amount to a massive timesink as they poked and prodded everything in sight, evoking exactly none of the tropes that drew me to Dungeons & Dragons in the first place. Despite this, you could say that at least traps cannot be simply discovered and/or ignored with a simple, mundane, convenient precaution.

Lurkers are part of a D&D monster subset of "things that pretend to be something else", in this case a ceiling. When you walk underneath one it tries to fall on you, tries to suffocate you, then I guess eats you or something if both things succeed. To mix things up, the trapper pretends to be a floor!

Not only are these things boring and exist only to mess with adventurers, but either of them will work exactly once before the party just starts peppering every ceiling and floor with ranged attacks to see if it bleeds. What makes the pair even sadder is that if they do discover it, it has no way to defend itself as they just calmly walk backwards while attacking. Or just ignore it.

The only thing I would change is making the trapper a kind of transmutation-trap. If a creature walks on top of it, then the floor moves to encase it Fullmetal Alchemist style. Though in some cases it might just be a slight inconvenience, it still makes more sense than a monster that exists solely to devour hapless adventurers.

I remember reading an ecology article on the piercer, which I found fascinating that anyone would bother writing an ecology article on such a thing, but still did nothing to endear it to me. The idea of a creature that lives underground and can only feed if a creature--not exactly a common occurrence underground--walks underneath it, gets hit by it when it falls, and is killed in one hit is even sillier than the lurker.

The darkmantle was a much more interesting and feasible creature, capable of actually moving and disguising itself as a stalactite. I would not really change it at all, but if I had to relate it to the piercer I would make it the second stage of a piercer's life, not the other way around.

Green slime works fine as a kind of dungeon hazard. I could see using it in encounters as something for the characters to avoid, or as an obstacle that they need to expend time and resources to remove. You could give it a recharging spore attack, or work it with other creatures like a stone golem.

I could take or leave shriekers. They make fine alarm systems, but are not very interesting or creative. I think that they would be better with some kind of sonic attack that deals damage or disorients you for awhile (thereby making you even easier prey for whatever might come along).

Ear seekers and throat leeches remind me of lurkers and trappers, just that instead of being created to inflict paranoia on adventurers by pretending to be something else, their crime is existing to force adventurers to add one additional step to a mundane quest. Listening at a wooden door? Use a metal cone with a mesh over it so that these things do not leap into your ear (which, as impossible as it may seem, is even stupider than the piercer's feeding habits). Oh, and filter your water, because Dungeons & Dragons is all about arbitrarily enforcing elements of realism. Except, you know, when it comes to infected wounds, internal injuries, malnutrition, equipment maintenance, and taking a dump.

Speaking of taking a dump, I am just barely okay with rot grubs, but more as a less immediately lethal disease-effect.

Finally, yellow and brown mold. Like the green slime, these things could work just fine as hazards, especially if it adds a tactical element to combat. I am even cool with the psionic variety.