D&D 5E A Massive Ritual

[Gilladian]

My PCs are attempting to stop a huge influx of alien beings from breaking through a planar gateway and invading their world.

To do this, they've learned that they must recruit a minimum of 20 3rd level or higher divine spellcasters to participate in a huge ritual to seal the gate and prevent the invasion. The PCs are 7th level, and have only 1 cleric in their party.

They've gone to one temple, and have been promised the aid of one high priest, and an as yet unknown number of lower level priests (I'm thinking they'll get about 5 more priests from this temple). Other temples in town will, if the PCs can roleplay things well, give them the other priests they need. However, I think I'll force them to have to deal with the priests of the God of the Dead (not always good, and not very popular) as well, to get their last one or two.

After that, they'll go back to where they need to cast the ritual. And here, I'm at a loss. This was very much a spur-of-the-moment idea, creating a ritual, instead of having the PCs battle the invaders themselves physically (it seems a much more permanent solution, to me, as well as pretty creative).

What sort of challenge can I inflict on the party to make the casting of the ritual difficult? I've told them that the aliens will break through in 72 hours, and the ritual will take 48 hours to cast; but I'm going to slow them down, further than they've been slowed down already, so that the two events are much more tightly scheduled; maybe so that a few of the aliens can get through during the ritual. But what else can go wrong? How can I set it up to be challenging and stressful, but still have their abilities affect the outcome?

The PCs are an eldritch knight (1/2 elf) folk hero, an elf arcane trickster rogue (urchin background) and a dwarf transmuter-wizard folk hero, plus their 4th level henchman war cleric (human), if that helps any.

 

[jaelis]

Making them protect the clerics while they cast is a classic. Maybe one cleric is a traitor and they have find out who and stop him.

 

[Lackhand]

Invading their world, or invading their nation?

Perhaps one or more of the priests are guilty of crimes in some neighboring nation, and NOW is when the Emperor-over-the-Sea sends his justiciar to execute his will and bring the accused to justice? Pleas that "this could be the end of the world" fall on deaf ears; the Justiciar is geased and truly believes that the will of the emperor outwieghs the good of a foreign (and unfriendly?) nation. Maybe the aliens will be better trade partners?

Perhaps the news that all these clerics are moving has piqued the curiosity of the thieves guild. That the right clerics in the right place under the right stars shall seal the breach is inevitable, but nobody said their jeweled altars would be safe when they got back. The characters have to scramble to solve the crime before the ritual is complete, or make powerful enemies going forward.

Perhaps the will of the clerics breaks and they start to abandon the project. There could be a saboteur, spreading dissidence for their own purposes; it could just be natural fear and regrets. Perhaps they need messages carried to their loved ones, or loved ones brought to them. Perhaps they want payment in goods or services to stay on the project. Perhaps they're sick and need medicine, or have a confession they need to unlabor before the world ends.

Finally: this is a big deal. If the party fails, the world changes. Big players are probably interested, both positively and negatively. Perhaps the party (as the harbingers of this change) are approached by peaceful emissaries of Heaven (the one-eyed beggar crone refuses to identify her alignment, but says the players must reject all reward and hold the gate; her presence keeps the other emissaries from acting openly), Hell (the charming cambion promises wealth and safety for the party and all their allies in the Iron City, if they can have the cast-off souls of the dead in the coming invasion), Ysgard (the valkyrie promises her sisters will hold the portal against all comers to test themselves in battle and produce more souls of slain warriors against the Twilight of the Gods; but the party does have to let the portal open to let that happen), The Abyss (a trio of unpleasant assassins who argue incessantly, and present themselves as in the employ of the death god to seed enough dissension to keep the ritual from going forward), and the Lords of Rule and Misrule (They cannot be told apart, but the lord of rule always lies, while the lord of misrule acts capriciously; order and chaos agree that Something Should Be Done, but not by the party, who should be removed first, so that order and chaos can act directly).

Good luck planning a session that can top We Stopped The End of the World. That risks being an anticlimax, when nothing happens (good )!