107th session of my Storm King's Thunder/Tyranny of Dragons/Scales of War mashup. Player characters started the session at 17th level, then hit 18th level, and reached 19th level by the end. I only allow level ups during long rests, which is what created the strange pacing. This session advanced and nearly resolved multiple dangling plot threads as we near the climax of the campaign.
The PCs have been playing through an extended dreamlike flashback sequence where the elf arcane trickster rogue learned that he and his evil twin sister are actually two halves of Erevan Ilesere, the elven god of trickery. Long ago, Erevan was caught looting Tiamat's treasure hoard on Avernus, the first layer of Hell. As punishment, Tiamat's minions executed Erevan with a mythic sword -- the mythic sword that split the dragon god Io in half, resulting in the creation of Tiamat and Bahamut. But Erevan didn't die. Instead, he was metaphysically split in two, and his two halves took mortal form in Faerun, with no knowledge or memory of their true nature. Now the rogue knows who he is...and who's responsible for making him that way.
Additionally, the PCs now know Tiamat's ultimate aim -- to slay Bahamut with the mythic sword and assume his divine portfolio, raising herself over all dragons across the multiverse.
Emerging from the dream sequence, the PCs found themsleves in the Temple of Mischief, a sacred place to Erevan. But they were not alone. Waiting in ambush for them were their clones!
To back up a bit, the middle of this campaign featured Manshoon and the Zhentarim as primary antagonists. In my Realms, there is (well, was) a true Manshoon -- with a near-infinite number of clones that were psychically connected to him. The PCs finally defeated Manshoon and his clones...but they learned that he had cloned the PCs. Finally, those clones have appeared. Their goal: Slay the PCs in the Temple of Mischief and absorb their souls!
Mechanically, I designed the clones so that when the clones took damage, the PCs would take psychic damage equal to half that amount. I assumed it would result in a very difficult fight. It did not. The players won handily through intelligent use of plane shift, forcecage, etc. The paladin's clone, ranger's clone, and sorcerer's clone were all quickly dispatched. Intriguingly, the rogue's clone was sent to the Astral Plane via plane shift. That's now a dangling plot thread that may or may not get resolved.
But then something interesting happened with the halfling bard's clone. The "real" bard is actually not what he appears to be. His body has been possessed by the soul of an amoral half-elf bard who died in battle with the PCs long ago. The halfling bard's soul is trapped in Hell. The other PCs have figured out most of this but have been keeping it secret while they determine what to do about it. Due to the clone's psychic connection to the original, he could sense something was wrong with the "real" bard and he blurted that out to the PCs, forcing a confrontation between the party and the possessing soul.
Concurrently, the half-elf bard's soul has been plotting to use wish and true polymorph to transform the halfling's body into a half-elven body. Which would leave the halfling's soul without a body to return to. But now...there's a halfling clone body with no soul. Which is kind of a great fit for a halfling soul with no body. It's like they were made for each other.
None of this was planned by me, by the way. It just...happened.
The PCs spent the rest of the session arguing with the now-exposed amoral half-elven bard (and each other) about what to do next. The more they talked about it, the more they decided he was more useful as an ally than as an enemy. So I think they're going to work together to get the halfling's soul out of Hell and meld it with the clone body.
Lots of unexpected developments!