What are some interesting monsters, plot hooks, or classes/abilities that could fit the "Broodmother" Archetype?

The drakainia. It's literally based on the "mother of monsters" archetype (drakainia is the "race" of Echidna, the ancient Greek mother of monsters and the original monstergirl).
Failing that, anything connected to Shub-Niggurath.

As for classes, an evil druid could fit to the sort of "corruption of nature"/"nature is fucking scary" archetype things like Shub-Niggurath tend to have, but there really isn't a good "broodmother" class unless you do some refluffing with something like thrallherd or a summoner class.

>punishing your players for being interested in their environment
It could be a neat story, but it sounds like you're training them to be unengaged murder-hobos.

Depends on whether it's treated as a hidden optional encounter, or a literal "you guaranteed your deaths by doing this thing you had no way of knowing would be bad" type scenario.

When the challenge is to "not get curious", I'd guess it's the latter. Especially if you're trapped during a snowstorm, so it doesn't sound like they can escape once they realise they're in shit.

Maiesta RPG.

There also is an official summoner variant called "broodmaster", which is centered around summoning multiple smaller and weaker eidolons.
Which incidentally is exactly how functions.

The whole Lamatashu thing in Pathfinder, Shub-niggurath, Dark young, Satyrs, Mother Hydra, Ragnorra, 2e-3.5 Vampires in correct hierachy set for spawn control, Slimes, that fucked up child that's evil and infest wombs in D&D shown in Cityscapes and Heroes of Horror, and those mockery vermin/worm things.

I actually rather like the way the broodometer class in Maiesta handles the summoner archetype, and the problem with action economy.
In most games summoned creatures will function like NPCs under the command of the summoner's player, with their own turns and action, which both bogs down the game and can cause serious issues with game balance as having more actions is generally extremely powerful. Maiesta deals with that by not making the summons attack on their own. Instead, each summon can add a die to the damage roll of a PC attacking a target next to them, increasing damage per round but not the amount of actions taken.

I wanted to write a class that functioned in a similar way (with different fluff, obviously) in 5th edition, but didn't have any ideas for different class archetypes (and I think I was also a few abilities short for the base class).
I should probably try finishing it.

There was a ton of silly shit you could do with Lunars in exalted 2E, especially with your Warform. I once built a honeybee Lunar that could lactate narcotic honey and had a Warform that housed hundreds of giant bees in her thorax.

>people actually talking about Maiesta
I never thought I'd see the day

Isn't there a goddess for that? Loviatar or Lamashtu or something? The only demon deity?

Yes, Lamashtu, goddess of monsters, beasts, bestiality, and that sort of things, who'se supposed to have given birth to a large number of monstrous races.
She's named after a mythical demon, but I don't recall the mythical Lamashtu being associated with birthing monsters. She just preyed on pregnant women and newborn children.

>classes/abilities that could fit the "Broodmother" Archetype?

Couldn't tell you at the moment, but I'll be monitering the thread.

I've got a pantheon of "Monster Gods" I'm working on and one is a BroodMother and I need inspiration for an appropriate spell pool of Miracles for her clerics and priests to use.

Well, I went and finished the base class abilities. However, I'm not sure what I'd do with the specialisations, which I'd need at least two of. The base abilities are rather dull as I intended for the more interesting abilities to go into the specialisations.
I'm thinking maybe one focused on healing/buffing, and another that focuses on fighting along with your summons (PC gains extra bonuses for damage when being around their summons).