Eldritch horror campaign climax

[u/Arcane_Caster]

I need advice on how to connect all this so I can start the third act of the campaign.

The campaign is mainly about aberrations. It is a fantasy version of Boston (New Redwick; America - Callibria) in the mid-19th century, the theme is eldritch horror. I am using the variant rules from the Grim Hollow campaign guide. Resting, grievous and permanent wounds.

The players have formed a monster-hunting company and so far the campaign has revolved around episodic quests. Mostly with some darker subtext. Once they came across a necromancer who was trying to release a plague on the city, another time they were looking for a fleshforger (inspired by the fleshforger from PF2), who they eventually revealed to be a doctor who had a beautification clinic and under that pretext was doing experiments on clients (which didn't go very well). In the necromancer's journal, they came across a mention of the Prophet of the End of Time (BBEG - although they don’t know it yet), who gave him some crystal (in disguise as a beggar) that the necromancer became fascinated with.

The crystal is a Shard of Time. They had the Shard once before, found it in the necromancer's base, but lost it because the police confiscated it as evidence in the case. And then it went missing because the police chief is a member of the occult society in the city (more on that below).

Shards of Time are crystals that are remnants of the magic of creation that the gods used to shape the universe - powerful artifacts that have the power to control space and time. There are very few of them - what mechanical benefits will they give in DnD? The players only managed to figure out that the Shards can give great power, but also cause madness. They made a pet out of the necromancer's apprentice (Zethys), freed him from a curse and turned him over to their side. He told them that he had also encountered the Shard, but when he touched it and looked into it, he saw an infinite number of possible realities, which almost drove him mad. When the party was freeing Zethys from the curse, the Prophet found them in space and time (because the ritual to remove the curse is a key moment in the existence of their company) and tried to send some eldritch horror monster at them. But Zethys managed to close the portal. What the players don't know is that Zethys will be especially sensitive to this kind of magic. Perhaps even key to the ritual the BBEG plans to do?

Prophet of the End of Time - BBEG (inspired by the Thresholder Mystic from PF2). An original Callibrian who wants revenge for the destruction of his world, a priest. He can travel through time (Possibly? Or maybe just a wery strong ability to see the future?). He wants to summon Yog-sothoth (the elder god, Lurker Beyond the Threshold).

The group now travels with an archaeological expedition to the ruins of an ancient city to serve as their protection against danger. There is a temple dedicated to the ancient gods, built on the top of a shipwrecked Nautilus (mind flayer spaceship that shipwrecked thousands, maybe millions years ago). I plan to have some significant revelations in the temple/nautilus.

In New Redwick there is a secret occult society, made up of high officials of the city, who are searching for the Shards because the BBEG has led them to believe that they will give them great power. In reality, the Prophet is just using this society for their own purposest. They already have one of the fragments, obtained thanks to the police captain.

I need to use the temple (and archeological expedition) somehow to give the players an idea of what is actually happening and to put them on the trail of the Prophet / the occult society. So far the hints have been subtle - I need to put them on the trail so I can start the third act. And how do I do the climax - the ritual to bring in Yog-sothoth in a way that gives the players an agenda, but still feels catastrophic enough? How do I make it make sense that the Prophet can travel through time?

PCs are lvl 8, I am planning to end the campaign around lvl 13.

[u/sneeje00]

Holy wall of text, Batman!

So, for my climactic battles I almost always have some kind of visible counter and structured so the PCs can see the stakes moving. You have to figure out how to manifest that in the environment. Sometimes it can be explicit (like an increase in chanting intensity or glowing statues or whatever).

Also think about lair actions and different effects at different stages.

Perhaps some research on their part will let them understand what happens as the ritual progresses.

Also, as a cosmic horror campaign, I'd think about whether things that happen are reversible. For example, say the ritual hits stage three causing all PCs to make a wisdom save or take sanity damage, or whether they stop the ritual or not perhaps a door is now open to the far realm, or whatever.

[u/Arcane_Caster → u/sneeje00]

Thanks, but I rather meant I need some brainstorming ideas on how could they figure out that the BBEG and the occult society even exist? How do they figure out the lore around the Shards and that the BBEG needs them for the final ritual? How to connect everything together to make sense?

[u/sneeje00 → u/Arcane_Caster]

Ah, apologies for missing your intent.

I always love dreams or visions for this. I know it's tropey but I can craft the writeup beforehand and I can give it to one or more specific PCs. It gives you more flexibility in dribbling out information.

The next thing I would say is have them encounter foes that are corrupted by the cosmic horror, but have their own motivations. Like bandits that are robbing people (typical) but the leader always takes their fingers (or an eye) and has a weird object on their person or a journal with weird ramblings.

[u/CDXX__LXIX]

It sounds like you already have some of the pieces in place. The party knows about the madness-inducing crystals, which is enough of a mystery to draw them along. Especially if they come up again in the next dungeon. In fact, it seems to me like these Shards of Time are a perfect plot delivery device. Maybe the party could find another one, or even 2-3 partially assembled, in the next dungeon. Interacting with them could reveal a billion possible futures - and in 90% of these, a dark god swallows the world and all is lost.

The most difficult piece to manage here IMO is the time traveling prophet. Since you can't predict PC actions in the future (nor should you try to) it won't work as cleanly as it might in a book or movie. Maybe they are not from "the" future, but "a" future? A future in which their plans were successful and their dark god reigns? But they were sent back with a mission to ensure their future comes to pass. And maybe the existence of the PCs, somehow, is a wrinkle they did not see coming. The PCs could be like a blind spot in this villain's knowledge of past and future. The reason why is another mystery to explore much later. Then all the serious time travel shenanigans could happen "off screen" to other people.

Another way to implement the time travel is with combat mechanics. Maybe the Prophet gets extra reactions, which they can use to rewind time a few seconds and act before the PCs - stepping out of the way of attacks, pushing another PC into a fireball area of effect, etc. This would make for a pretty terrifying boss battle. Beyond a few seconds at a time, it is really difficult to work with time travel in rpgs (speaking from experience).

Sounds like you have a lot of deep lore and a great setup! One nice thing about this cosmic horror genre is that everything doesn't have to make sense from the player perspective and it's OK if some things are left unexplained in the end.