#RPGaDAY2018 - Day 15: Describe a tricky RPG experience you enjoyed

I've been talking about my crown jewel of campaigns, Eberron Unlimited, these past few days, so I recommend you read these posts if you haven't so you understand what made this one so special.

tl;dr Eberron Unlimited was a 10-session, summer campaign composed of three different adventuring parties, each with their own dungeon masters, playing at the same time, in the same world. Each of them had their own story, with an overarching plot that tied the three of them together, eventually leading them to meet and join forces against a common threat.

One of my few regrets is not being able to fit this bad boy in the story

In today's answer, I'd like to talk about Eberron Unlimited's Last Session. What made this session so tricky was that I had to DM it all on my own, as my fellow co-DMs were unavailable for the send-off of this campaign. This meant that I had to run for three groups of 4 - 6 (for a total of 15) players at the same time, and give closure to each of their storylines as well as the overarching storyline. Sometimes they'd have to split up and I'd need to run them one by one, cycling through them. This took place in the span of nearly 20 game hours between the weekend (we slept in the middle of it); We decided to spend the night together at a player's house as part of one big concluding event. It was crazy!   

Here's a summary of what I remember of it:

The Progeny of Syberis (PoS), Children of Eberron (CoS), and Spawn of Khyber (SoK), had joined forces against the Lords of Dust, fiends that plot in the shadows, looking to bring back their masters, the Rakshasa Rajah, one of which was on the verge of reanimation: The Lord of Dreams.

Eberron put Rakshasa in a position of awesome

Once the three groups entered The Lord of Dreams' realm to stop The Lord of Dusts' ritual, they went through a series of puzzles until they each reached a member or associate of the Lords of Dust, in the process of finishing the ritual. The Children of Eberron, however, met with Mordain the Fleshweaver, pet monkey and everything, who had taken down a member of the Lords of Dust in an attempt to graft himself on the Lord of Dreams.

Eventually, even though the ritual was stopped, Mordain managed to siphon power from the Lord of Dreams, and proceeded to attempt to finish the three groups off so that his plan to become the ultimate being could come into fruition, uninterrupted. It turned into a one-round encounter where every PC blew all their resources into knocking him down before he dealt them all a devastating blow. 

In the end, the PCs managed to save the day, though the world of Eberron was changed by the machinations that transpired along the game. Every player described as how their characters would live out the rest of their days, and that would be the last they would know about this Eberron story.