damn thats just straight up evil lol. I wonder if its possible to survive this. I have a question on that. If somehow, by all weird odds. Manage to get 1 pawn alive. Would that pawn automatically die or just left alone in this hellish world?

Well, if you were to do something like dev mode resurrect - yep, they'd be alone in a doomed hellscape. :)

Seems kind of boring to just be over. In my opinion this'd be much better if it kept the end of the world scenario, but left the pawns alive to struggle though the apocalypse. And perhaps instead of destroying all settlements every faction could be forced into permanent hostility.

In order to truly destroy the player, perhaps the Grimoire acts as a beacon and forces constant raids. This could be paired with it giving incredible physical, mental and psychic buffs to people who read it, but not fully, acting as a tool as last resort and giving it some allure. It could also be the focus of mental breaks, calling out to people in their lowest moments, having them unwittingly bring about the end.

Whilst it's fine for the Grimoire to act as a game over item, the result should come as something the player can struggle against in vain, seeing the consequences of their actions, not a world instakill. If the player can continue however, the Grimoire should probably disappear and catch fire to stop it being reread for more bonuses, similar to the codex of wisdom.

It also doesn't need to be permanent. If there are short term benefits to reading it, just a quadrum of disaster could be equally bad, granting an immediate reprieve from your situation only to give you a slow, drawn out end. If you cannot grow crops due to an eclipse, and are having to constantly fight against raids and infestations, with earthquakes threatening to destroy your defences, it is only a matter of time until you fall, and if you somehow survive there would certainly be a long way to go to rebuild.

In addition, the codex of wisdom seems somewhat overpowered. Perhaps make it the focus of a special journal quest, and change its effects to either max out a single skill or grant an immense learning boost for a quadrum or so?

Good ideas and feedback. Yeah, the codex should probably max a single skill.

I like the idea of doing something more with the factions - perhaps some randomness, destroy half or a third, turn all the others hostile.

You have definitely provided a lot of good ideas for fleshing this out and making it more of a game system rather than a proof-of-concept, "what does it take to render Rimworld inert?" thought exercise. :) Greatly appreciated!

I have pushed an update to nerf the Codex, one random skill gets maxed.

I would LOVE to see the grimoire be expanded upon, if only slightly. It doesn't have to kickstart a totally new set of rules, but there is just so much potential in the possibility of playing on a dying planet rather than one that's already dead and completely inert.

Say, that effect of the Grimoire reminds me of what happens when you finish your first Genocide run in Undertale. Permanent dark, rainy thunderstorm (very windy), and absolutely nobody left alive from ANY faction. All it’s missing is a twisted specter demanding your soul in exchange for restoring the world.

And speaking of grimoires, how’s progress coming on that Call of Cthulhu—Cults update? If it’s not too much trouble, I have a request related to that question: Could I please get a notice when it’s done?

Someone's gonna destroy their save because of this book. This thing better have a warning sign.

Too bad for them I guess. If they don't read the mod page, don't read the book description, allow a pawn to read the book while thunder and lightning rage around them and I send message after message warning them ... they get to enjoy their broken game state (the save itself is not broken unless they are even more foolish and SAVE after the doom).

i wonder; if you do end up reworking the grimoire to be a nigh-unlivable apocalypse rather than an instant game over, when will a streamer do a challenge run with said ruined world?

Couldn't say! I don't really pay attention to streamers/influencers/salespersons.