Think of Primus as an incredible artificial intelligence, maybe picture as a brazen/brass head made of extremely sophisticated clockwork mechanisms – like Wizard of Oz, but behind the screen are just more and more sophisticated mechanisms.First up, if you're playing in my "Augustus Giovanni Must Die" campaign, GO AWAY.
No really. Kick rocks.
Alright, so the city in my current sandbox urban campaign is menaced by crazy sewer people empowered by a rift to the Far Realms located deep under the sewers. My PCs want to close this rift for various reasons. One of them asked me once, "Hey, is there like a god of order?" and I, being a dummy-McDum-dum, said, "Well, there's Primus. He's the progenitor of the modrons and he lives on Mechanus." And my player was like, "Cool, I want him to help us close this rift."
And now I'm like, "Uhhhh...."
So my initial thought here is that Mechanus is dealing with some kind of threat that has absorbed Primus' attention. If the PCs can make the threat go bye-bye, Primus will grant them an audience.
So I need something so powerful that Primus can't not deal with it, but not so powerful it will wipe out my 13th level PCs. My initial thought is that there's a slaad invasion, and they're empowered by this Chaos artifact that's creating a beachhead onto Mechanus. Primus and the modrons are busy dealing with all the foot-soldier slaad who are running amok through Mechanus, leaving no resources free to take out the Chaos artifact.
Cute modron mascot for potential party adoption
Helpful djinn (planar merchant) who can explain the situation to the PCs
Strike teams: 1d4 red slaad, 1d4 blue slaad, and 1d4-2 green slaad (encountered en route to artifact, half hp and spell slots)
Defending Chaos Artifact: 1d6 red slaad, 1 blue slaad, 1d4-1 green slaad, 1 grey slaad (plus random battlefield effects from Chaos artifact)
Reinforcements From Limbo: 1d4 red slaad, 1 green slaad, 1 grey slaad, and 1 death slaad (appear as PCs go to take control of the Chaos artifact)
I would love input on 1) how reasonable this setup is for a group of 5 13th level PCs (sorcerer with no damage spells, twilight cleric, Mercy monk, Bear barbarian, and swashbuckler rogue), 2) Setups y'all think are better than what I laid out, 'cuz I need all the help I can get, 3) Ways Primus can help the PCs without just solving the problem for them.
What would trouble an AI to the point that it would seek out flawed emotional mortals to complete a task that neither it nor its constructed minions can attend to?
I imagine anything tainting its processes would be a prime example – Primus discovering love and needing to wipe its memory of love which leads to bias and chaos, or some kind of a special Chaos Shard weapon being dropped into the heart of Mechanus by Kyuss worm-infested shapechanging green slaad (sort of a mirror of the Law Shard or whatever it's called that 5e Primus thrust into Limbo), or a battalion of rogue modrons who know a magical secret that corrupts any modrons coming into contact with them like plague-carriers.