The Perils of the Hellfire Approach
Consider the adherer. Or, if you like, the nilbog. Or the pseudo-undead.
The what, the what, and the what?
Well, that’s kind of my point. Old-school gamers may remember the adherer. Fewer will remember the nilbog and pseudo-undead. I could have listed the gas spore, and more people would know what that was, but even then, I suspect many readers would have to go flip through the book.
All of the above critters are Gotcha monsters, just like Hellfire’s fire-loving troll.
Each Gotcha monster was designed to trick players who already know what other monsters look and act like. The adherer looks like a mummy, but isn’t undead and is very sticky. The nilbog looks like a goblin, but reverses entropy. The pseudo-undead look like skeletons thanks to translucent flesh, but surprise! — you can’t turn them. The gas spore looks just like a product-identity creature I’m not going to name, lest the cover of one of my rule books animate and attack me with three eye rays a turn. Hit it with your sneak attack, and you get a face-full of toxic spore.
Chances are pretty good that most of you needed at least one of those descriptions.
Why aren’t the Gotcha monsters better-known?
Well, first off, they serve no ecological or story-related purpose other than to trick players. Once you’ve used them, there’s not much point in ever having your players encounter that creature again. Note that I said players, not PCs. In more than three decades of GMing, mostly with the same group, I think I’ve used each of those monsters exactly once. Once my players knew the trick, there wasn’t much point in repeat appearances. However, I’ve reused trolls and liches and other monsters many times each. In short, each Gotcha creature is a one-shot monster-of-the-week.
The bigger problem is that Hellfire is a flaming hypocrite. He’s responding to meta-gaming with meta-GMing. And his meta-behavior is worse, because it does more to disrupt game immersion. As soon as your cackling GM unveils the Gotcha, you know you’re dealing with an adversarial dude who was out to teach you a lesson. It’s not organic to the game. The GM is responding to a sin with a sin or two of his own.
It’s tough to teach players to immerse better while ripping them out of the game. If you want them to immerse and role-play, you need to set an example by being immersive and realistic yourself.