I finally dug my 3.5 monster manual out of the box so I'll probably talk about monster's 3.5 incarnation if my chosen monster appears in both.
3HD monsters with an armored head, soft body, and 8 paralytic attacks per turn. While modern interpretations tend to have caveats like
No matter how many of a tentacle worm's attacks hit an opponent in a given round, only one saving throw is required in each such round (BFRPG)
The AD&D manual doubles down and just says "As there are so many tentacles with which to hit, and thus multiple chances of being paralyzed, these monsters are greatly feared." Just a flat acknowledgement of 'yeah your players SHOULD be scared.' Given that they also show up in groups of 1d6, this is the sort of creature that really emphasizes how combat was not meant to be a honorable affair of standing face to face trading blows until one party was defeated and showing off your cool combat maths.
They've got Treasure Type B, which is potentially pretty good, but also unreliable, which makes sense- maybe they've dragged a bunch of gold-ring wearing nobles down to their lair, maybe they've just been eating giant rats.
The 3.5 Carrion Crawler is similarly deadly at first glance, but closer indication reveals that the paralysis DC is 13, which is pretty pitiful, and the duration of paralysis is a mere 2d4 rounds (no mention of duration is given in AD&D). Of some interest is the notes on behavior- the AD&D version mentions they are scavengers that will happily turn predatory to make corpses to either eat or lay their eggs in, the 3.5 version differs with them immediately turning to devour the paralyzed with their feeble, inaccurate bite, and that 'multiple crawlers do not fight in concert,but each paralyzes as many opponents as possible. The unintelligent creature continues to attack as long as it faces any moving opponents."
Them only attacking you if you move is good monster stuff, though the direction given in the more modern bestiary is clearly more tactically than strategically focused, given the lack of mention of egg-laying or scavenger preference.
Sunset Realm Sewer Snatchers