Status: D&D related, possibly obvious
Vermintide 2 was free on steam the other weekend and my brother and I have been playing it together. We've been trying to play it with the mechanics unspoiled to keep a bit of sense of wonder/surprise in it.
Something that stuck out immediately was the special enemies. This is really a common design pattern in team horde FPSes - Left For Dead and Deep Rock Galactic both have analogs (and I like DRG's term for them - "disruptive" enemies). These enemies either deny you terrain and visibility (with, for example, a big cloud of poison gas) or suppress/disrupt an individual player (for example by grabbing a character, preventing them from attacking, and dragging them away from the party) until either the target or the special enemy is killed. They aren't especially tough and their damage output isn't enormous but they require pretty immediate action or they can seriously degrade the party's ability to fight the horde of fodder enemies who usually accompany them.
Vermintide got me thinking about this from the D&D angle for two reasons - first that unlike DRG it is low-ish fantasy, and second because it makes these special enemies very high-visibility. The player characters call them out in game (at least on the difficulty we're playing), many have literally high-visibility glowy bits, and killing them is mentioned in the post-mission statistics screen, which makes it clear that they're thought of as a class or category of enemies.
(The other two called-out classes, Elites and Monsters, also bear consideration. Elites we think are tougher versions of normal enemies; they may be better armored or hit harder and bear special consideration on those accounts but they're not especially disruptive to party cohesion / positioning. Monsters are creatures much larger than a man like trolls or rat-ogres that, as least as far as we can tell, require pretty much the whole party to fight them concurrently, with lots of HP and a boss healthbar, and often a combination of multiple damaging attacks, throws, grabs, area denial, and other abilities that you might expect of a Special but on a much beefier frame)
Meanwhile, in OSR D&D, we have critters that have disruptive abilities like a Special but we're mostly not using them in combination with regular enemies. Consider mummies. Mummy paralysis is a big disruptive ability and anybody left with freedom of action has the onus on them to kill the mummy immediately (or at least bait an attack out of it) to end the paralysis. But mummies are their own monster type with their own lairs and if you're stocking by the book you're never going to get an encounter with 15 zombies or skeletons and one or two mummies - the fodder+special combo. Or, if mummies are too high-HD and durable and fall closer to the Monsters category, 15 zombies and two ghouls. A gelatinous cube plus a bunch of skeletons would be an encounter to remember, but it won't ever come up in prep (though it could potentially happen in play through a combination of a fixed skeleton encounter and a lurking threat cube making its move as the party is dealing with the skellies). The best we've got are witchdoctors and shamans with beastman lairs - and those are wilderness lairs, not dungeon encounters, and if you're rolling random spells for your witchdoctors they're usually either duds or TPK threats instead. In beastmen too we have something like Elites in champions and chieftains.
But the fodder+special combo seems like the sort of thing you'd want to use if you were building dungeons to challenge your players. And this whole line of thought also ties back to breaking up the phalanx - enemies who deny choke-points, grab front-liners, or bull-rush through them, all seem like good tools for diminishing the power of the shield-wall in the dungeon, but I haven't been thinking of them as a category.
Is this too 3e a thought? Is this something 4e did explicitly? Does this place too much emphasis on tactics of individual combats in OSR games where combat options are relatively scarce so parties may not really have any means to respond to disruptive enemies - games where the emphasis is generally on the expedition as a whole anyway? Is this even worth considering in prep or is it good enough if it can happen randomly in play? I really don't know. But it might bear experiments, and seems like a useful schema / category with which to think about monsters in tabletop games.
Beastman chieftain abilities might be a really easy place to start with procedurally-generated fodder+special combos. One could design abilities with the special/elite distinction in mind, and then push them down to subchieftains so that they start showing up in dungeon lairs.
Maybe another angle to consider is strategically-disruptive enemies: expedition-disruptors rather than single-combat-disruptors. If the focus of the game is on the expedition and we're worried about there being too few in-combat options, maybe it makes sense to shift one level higher. The Crypt Thing might be a really good example of this - its teleport doesn't just take a character out of a particular combat temporarily, but disrupts the expedition as a whole by scattering the party throughout the dungeon.
But what does combining expedition-disrupting enemies with fodder look like? Maybe just random encounters being triggered by a disrupted party taking more time to recover. Maybe nothing at all needs to be done and OSR D&D is just fine the way it is.