A direct call into minds of demigods of Corruption

[HoboKnight]

Hey,
my party got their hands on herbs that enable contacting a trio of demigods of Corruption in their demiplane. You place herbs on fire, get stoned and part of you is mentally dragged into their demiplane. Direct contact to their minds.

Usually, herbs are used by evil hags and cultists of Corruption, this time it will be one or more paladins.

PCs will get a disturbing insight into the minds of demigods, also some saves to ward off madness effects. (It's a bit like connecting to "the other side" in Event Horizon")

Fluff: how do I make this as disturbing as possible? They are entering minds of Hags from Witcher/Hannibal Lecter/main antagonist of True detective/Mister C./dark Dale Cooper from Twin Peaks se2?

Mechanics: madness saves. Should I add anything else?

Demigods reaction: these guys have a number of cults all over Material plane. Their followers corrupt and torture people, with an emphasis upon children. And at this point, someone picked up a phone, who is NOT their follower. Demigods may not care much about their fillower cell being destroyed, but for them, such a call is upsetting. What should their reaction be?

Thanks!

[Vahnavoi]

If you want to do something upsetting, you need to seriously ask yourself: "what do my players find upsetting?"

Then maybe do an image search on those subjects, and make up your mind on if they're too upsetting to you to include.

Mechanics? Mechanics are unnecessary. Anything that freaks out your players to even a slight degree will affect how they play their characters. The question is, do you want them to do something specific, or is any kind of reaction fine?

This said: to some players, what upsets them is the mechanics. To give an example of a videogame, sanity effects in Eternal Darkness: Sanity's Requiem occasionally break the fourth wall and screw with the player directly. Muting the sound or making it look like there's a fly on the screen, are milder examples. One that elicited a genuine scream of horror from a relative of mine? The game, apparently, glitching and deleting their save file, despite them choosing "no" in the dialogue prompt "Delete all save files?"

So if your players are irrationally attached to their play piece's equipment, sanity points, experience points, whatever, do at least go through the motions to threaten those.

Moving on. It's hard to say how the demigods should react without knowing more of their characterization. The fact that you're here, asking, suggests you don't have a good idea of that yourself. You can take some cues from any tripartite mythological entity, including invented ones like the trio of gods from, say, Eternal Darkness.

One, core idea: do make them different.

If at all possible: make them appealing and repulsive in different ways. Preferably, so that they're appeal and repulse different players.

More specific advice pending your answer to the first question.

[Slipjig]

What is the goal of the demigods in question? Your PCs call it "corruption", but the demigods might view their mission as the riotous expansion of life, creative freedom, a necessary counterweight to the ossification of the Old Ways, or breaking the chains of convention.

Maybe their cultists were TOTALLY wrong about how they want to be worshipped! They don't want torture and child sacrifice!
They want the PCs to come work for them, overthrowing the current unjust power structures so that radical egalitarianism can flourish in it's place!

Figure out a message that will appeal to your PCs, and sell the hell out of it. If the power structures in your world are ACTUALLY corrupt, so much the better. If the power structures AREN'T actually corrupt, the demigods show them false visions "proving" that their patron or various authority figures are corrupt.

And they'll close by offering the PCs a taste of their power, if they promise to go use it overthrow the corrupt. The demigods don't even want the credit! They just want to help make the world a better place!