Main Menagerie Storyline

Based on the party's history, their travels, and an understanding of the world and its myths, this is a write-up of what they seem to believe at this time. There are still gaps and questions, obviously – but hopefully this helps translates conversations and character knowledge into an understandable sense of the world as it is right now.
Myth, possible history it seems: Long ago before this world existed there was another world here. That was Toril (aka the Forgotten Realms of D&D lore). Something caused that world to be destroyed, but early in its history there was a culture of man known as the Netherese. They had performed a ritual which would grant them power and knowledge, and all they had to give up was the world of Toril in its last days. That would preserve it as a "Gem of Tharizdun". If 333 such worlds sacrifice their world in such a way and those gems all end up in the same realm it will be possible to free Tharizdun, one of the very first entities and one that stands for chaos and destruction. It is believed at that point he will be the ultimate power and able to shape reality however he wants.
Something that has only been hinted at, but it seems that when the Netherese' culture was in its last days it triggered a variant of that ritual they had long ago performed. It sent many of their more enlightened and powerful far into the future where it would be safe for them to rebuild again. That future was on Dierde, as it sits in the place where Toril once stood only far far far in the future.
Dierde is a world built on the empty shell of embers that was once Toril, built by D’erletztesøhn, a Dragon god who sought refuge from the gods in his realm seeking his destruction. He was gravely wounded and found this empty place. He formed his children to guard him as he rested and recouped his strength. He is the Sun and is resting – trying to recover from the grievous wounds he long ago received. The children, now the planets, are here to watch over him.
Long ago an event occurred that convinced the Dragon That Slumbers inside of Dierde to wake up – that event had to do with the Gods and Deities from all over having too much access to this world. At that time many of the more powerful, the more adventurous, and those willing to make sacrifices came together. They used the Arcane Forges to make great weapons to stop the Great Dragon in the Earth. They were successful, and it meant the gods had to leave this place leaving only a few possible ways to have influence or gain power from this Realm. For all intents and purposes, they are essentially banished or risk the destruction of the world. This was the Great Sacrifice.
NOW, the party is also learning how part of that event had chromatic dragons sent from the opening in the Earth that went after the Arcane Forges to destroy them. They seemed to have been stopped at some by a group of Metallic Dragons that have since protected these forges with simulacrum polymorphed as the chromatics.
The party has also had a lot of problems it seems with the Arcane Order. This is a very secretive and powerful organization made of spellcasters and mercenaries that seeks items of power. It also seems that part of the initiation is for the caster to prove their future power by a ritual that summons their future self. That future self will cast a clone spell and a simulacrum spell so that if they die, they can be resummoned and attended to. This is what happened with Jacoby. After the party killed him, his "soul" returned to the clone-body-in-waiting and he was raised up. In a younger form, no less – something the clone spell allows.
Jeets and his current party, the Misfortunate Mead Heroes is comprised of two half-elven twins from a village destroyed, a man claiming to be a Bronze Dragon (the same one which stopped the White Dragon, Canthenth at Outding Refuge, and then replaced him with a simulacrum polymorphed to a White Dragon.) The last group he was in, the Fortunate Mead Heroes, saw Talbron and Cellymas dying in a fight with Bargle and Pradam retiring and working with Lars & Ursa at whatever magical lab they have built in the past few years.
The Misfortunate Mead Heroes is seeking out Jacoby and the Mindflayer, Gruzzussk D'Achtend, due to their mindcrystal messing up the simulacrum's brain. This brought them to the keep where the Menagerie were. They also had a dagger crafted by Lars similar to the one which the rest have, and it didn't come up in the game – but it was commissioned by The Elder as a gift for Calliope.
So, the main problem seems to be that a few of these orbs are appearing on Dierde and that could possibly mean this is the last world before Tharizdun destroys everything. These orbs can grant a lot of power to those who wield them, but it also heavily corrupts them. The Order wants them, for the power and possibly hoping they could get more power if they help Tharizdun.
It also seems that Grognard, aka Captain Meklan, was leading an adventuring party long ago – around the time of the last awakening, the Great Sacrifice. Him and his party, which includes some people known to the party helped stop the Evil "unnamed" Archfey which tried to create a Material Plane/Shadowfell place. Instead they created the Skola Vale as a place between the Feywild and Material Plane, this act also created the Elder as a protector of the Vale. She was created in that process and she is tied to the place.
Underneath the village and the corpse of the Evil Archfey there was the Temple of Tharizdun, this was a place of great evil so it was locked into a pocket dimension in those days. Locked ever since until Bargle hired a bunch of mercenaries to attack the Vale. That triggered a protection spell transporting the Vale to the Feywild. It also allowed access to the temple and the ship, the ship was holding an orb… but Bargle did not know that Bast had already come here and taken the orb. Handing the orb to a Tortle hermit, Sas. She needs that orb to get to the City in the Mist so it can aid a dying pharoah she wants saved.
Another orb was in a magic cap that Pradam Estorich possesses. Since the "Mead Heroes" stopped Bargle and gained his orb they seem to have access to two of them they have hidden away. Pradam is from "another world" where he lost his friends in a fight to Venger. That realm of Venger's wasn't actually Pradam's world, as he had found himself transported there one day – these are facts not explored by the party and may or may not have anything to do with the issues today. Bargle is also from "another world", he is from a world called Mystara and he wants to return, but not empty handed. He seemed intent on finding a second orb – so he could use the destruction of one to send him back holding the other orb. That would mean he could return with all the power in an orb.
Bargle now seems to be a Lich, and still working with the Arcane Order, the Blood Hand Orcs, Jacoby Drexelhand, and the Mindflayer (Gruzzussk D'Achtend). Probably still seeking the orbs for his own means, but convincing the Order he seeks to help them in their goals.
;TLDR: Dierde sits where Toril was. Toril was destroyed (somehow), but that destruction triggered an ancient spell from the Netherese given to them by Tharizdun. This is how Tharizdun seeks his freedom. He needs to corrupt 333 such worlds and have the gems all in the same Realm.
The Arcane Order seeks these for power, and to help Tharizdun. The AO also are hard to destroy as they are very powerful wizards and manipulate clone spells, simulacrum spells, and chronomancy. Jacoby and Gruzzusk (Mindflayer) needs "the tortles" (Sas and her father?) and "the book" (Grognard's Journal) for some purpose. Bargle seems to be seeking the orbs for his own power, he is now a lich.
This world is already destined to become an orb, since the Netherese of Toril came here. It is also possible that the AO hopes to waken the Dragon in the earth as it will lead to the planet's destruction -- meaning it will become an orb.