Ear Seeker (From AEC)
No. Enc.: 1d4 (1d4)
Move: 10' (3')
For those of you not familiar with this critter, how on earth did you end up reading this blog??
Basically, it's a little bug that burrows in wood, but looks for a nice warm body to lay its eggs in. The classic trope is a wooden door in a dungeon. When some hapless PC listens at the door (like ya do), The little bug crawls into the comfy ear and gets to work. When the eggs hatch, you've got 1d8+8 hungry larvae. Guess what THEY like to eat? (Hint: It's not strained beets.) Brains and flesh, basically.
Remember Wrath of Khan?
Yup. Basically that.
The book says 4d6 hours until they hatch and then it's 90% fatal. That's right, a percentile roll, NOT a saving throw. Cure Disease handles the problem nicely, but the wording of the monster description is unclear how obvious it is to the victim that anything is wrong, or how long after the eggs hatch that the PC may die. In real life, people get infected with parasites all the time without knowing it. I think, to be fair, I would give the PC a window to notice some extreme discomfort for a bit before they keel over (maybe a couple of hours). That would give a cleric a chance to effect a cure.
I say "fair", but the very nature of this monster is somewhat unfair. Or at least, it would need some setup to make it more reasonable to throw at a group. It's tailor-made to punish players for exercising caution in the dungeon.
PS: It occurs to me that a paranoid noble might deliberately place the creatures in his doors to punish eavesdropping or to catch/identify a spy.