Did they release a 5.5 PHB

Pretty much

3.5 crunchy

Naaaaaaah.

Congratulations! Your players have become the villains of the campaign. What should you expect when this happens?

Well, summoning an elder god is an extremely stupid foolish idiot thing to do. An Elder God cannot be reasoned with or controlled by a pathetic mortal and attempting to get its attention will likely get a dozen square miles flattened like God swatting a flea.

But if you’re arrogant or greedy or shortsighted enough to want to do it anyways, then you’ve got a lot of work to do. At the very least, you’re going to need a complete copy of the necronomicon, which will be near-impossible to find and definitely impossible to retrieve without committing some heinous crimes. Plus you’ll need some ritual artifacts from cyclopean remnants deep beneath the sea or under the ice in the antarctic. And to get all those, you need money, power, and connections so I hope you like dealing with the Mob. Plus your body will need to be altered to survive channeling that much arcane power, so I hope you like mutating into something that makes Wilbur Whately look like Adonis.

And naturally while you’re doing all this, a group of random shmoes will stumble onto your conspiracy and band together as a group of Investigators to try and stop you beginning an apocalypse. There’ll be some back and forth as you send minions to deal with them, trap them, race them, etc., but they almost certainly will be there right as you are culminating your great summoning ritual. Then it’s all up to the dice: either you win, summon an Elder God, and get everything in the zip code including yourself killed for annoying it; or you lose, and an investigator puts a .44 through your soft cartilaginous skull.

I’ll take any opportunity I can to link the legendary RPG.net review of FATAL.

https://www.rpg.net/reviews/archive/14/14567.phtml

I wish this post was twice as long and went way deeper into each category with examples and use cases.

The discussion around the “Fruitful Void” and Brennan’s initial comment made me think specifically of this story from Chocolate Hammer where a highly-random, highly-lethal small-scale cowboy wargame ended up being an extremely fertile ground for interesting stories despite having no narrative mechanics of any kind.

A system specifically focused entirely on combat gave the GM room to weave a vast web of intrigue and personality based on how everyone knowing the power of violence in the system and trying to avoid getting near it while using it to threaten everyone else.

I’d imagine it’s the OSR influence, especially with the more old-school notion that the random encounters are the story.

That is, instead of random encounters being an interruption of the narrative, they’re just as much a part of it as the time your PCs sat in a bar for two hours trying to convince the barmaid to go dungeon-crawling with them.

Especially if random encounters include variation in distance and attitude. Encountering a knight could involve stumbling into a questing hedge knight‘s campsite, or it could involve hiding from the Black Knight after spotting them from a nearby hillside.

And there is also a narrative purpose in having combat start from “just existing in the game world.” Parts of the world are dangerous and deadly to be in, and random encounters are a good way to portray that without elaborately plotting out a sequence of “dangerous events” on a travel timetable.

Any sort of character concept that depends on witholding information from the other players is extremely difficult to do in a satisfying way.

The other players can easily not care about your mystery at all, making your secret just you and the dm making eyebrows at each other. Or they’ll care more than you want, and any sort of long-term intrigue goes out the window as the party drills into your character. Or hell, maybe they’ll be annoyed that you’re being so coy about your character, maybe they’ll find it shifty or frustrating or any of a dozen other things. And even if there’s the perfect level of investment and buy-in from everyone else, it still runs the risk of being a spotlight hog of a character.

So generally it’ll either have absolutely no impact, or it’ll derail the party.

Oh, and all of this goes for double if your secret is that you’re working against the party.

I’d be interested to see The Sprawl or Blades In The Dark’s “planning” mechanics applied to an oracle.

The Soldier playbook in the Sprawl gets to roll at the at start of each job to determine how many bullshit points they can spend during the job to get where they need to or have something they need.

Alternately if you like vague prophecies I’m picturing a system where at the start of the adventuring day you roll on a table of prophecy fragments, each with a mechanical effect, and the more powerful you get the better effects you can have and the more fragments you can roll for. That way you can have vague prophetic words that have a mechanical effect for you to play the hand of destiny.