2 spaceships crashed on the planet of Humblewood, alerting some humblefolk residents. Plus, 2 players teleported onto there from Faerun. 

They disturbed Lord Brisbane who sues them and the town complies. 

The party moves to the mountains toward the wreckage, to prove their innocence, but get caught up in a collapsing mineshaft. 

They link up with the owners, a Bandit organisation in Camp Crest. There, someone else has surprisingly taken control of the camp!

The new camp leader is the Giff Geoffrey, who sends the party to reclaim advanced tech from the spaceship wreckage.

At the wreckage, the party learns of another bandit camp taken over, they find the ex-leader mind controlled by alien and hostile Neogi, and a yellow crystal formation that is rapidly growing, threatening to engulf the wreckage. 

Xaryxis is a dying star. the Xaryxian elves feed it other planets to prolong its existance, by infecting other worlds with yellow crystals. These crystals are transported by their fleet and are helped by mercenary vessels. One such vessel is an Uspo owned by Oswald cobblepot, a villainous Dohwar tradesman (compare him to a Rogue Trader in 40k). While transporting one such crystal, the Uspo gets attacked by a Deathspider vessel from the Neogi Sisk Illigar. The vessels entangle in close combat, careen into a nearby realm and crash on humblewood's Crest Mountains. Many crew perish (about half of each ship). The Dohwar hole up in the Mountains, sending out their allies (the Giff) to quickly provide a means to leave the planet. They need a workforce, resources, a plan, advanced tech and a launch site.

1 - Workforce: humblewood folk (currently employing Bandits, but more workforce is preferred from the Greater Humblewood)
2 - Resources: mining, chopping wood, spellcasters for conjuring, trading
3 - Plan: The Dohwar are geniuses and have this in order
4 - Advanced tech: Obtained from the ship wreckages, or stolen from the Neogi
5 - Launch Site: ship building infrastructure is mainly in the Harbor of Saltar's Port unless Gardenport/heartmouth/Alderheart can be improvised

Issues:
1 - Disease: 30% of the current workforce is infected by a fungal disease, rendering them unable to work. Either new employees or a cure is found. Deal with this or lose precious time, putting the rest of the mission (halting the star) under strong time pressure.
2 - Politics: Trading is hard, the Vulpin and Hedge Elite (Lord Brisbane + associates) will do everything in their power to maintain their positions, wealth and influence. Deal with this to secure the resources.
3 - Neogi: They are out to kill your ticket out of here. Keep the Dohwar alive to get off the planet.
4 - Yellow Crystal: Its growth cannot be stopped. It will consume this world unless the star of Xaryxis is dead/disrupted. Deal or lose Advanced Tech option.
5 - Guild dynamics: Earn guild respect to use the port shipyard.

SPELLJAMMER ARC

the Xaryxians plant astral seeds on Toril to harvest the planet’s energy in order to feed their own dying star. Up until now, they have only harvested uninhabited planets, but because Xeleth and Xedalli want more power for themselves, they have decided to target a living world.

The prince and princess want more than just a thriving star for their people, they want power for themselves. They create two starlight rings that divert a portion of the harvested energy into themselves, effectively making themselves immortal.

The twins were meant to rule together and share the power, but Xeleth betrays Xedalli. He frames her for treason and she is banished from xaryxispace, so that he may be crowned instead. Xeleth believes that he destroyed Xedalli’s ring, but it was only a clever copy. Xedalli still has her own starlight ring, which Xeleth will eventually realize.

When the characters find Xedalli aboard the Last Breath, she will play the victim and will use the party to get back to Xaryxis and hopefully kill her brother. She claims:

• The Xaryxian empire drew on their own star to supplement their magic, and it eventually started to dim. They harvest other planet’s energy to keep Xaryxis alive. (true)

• Her evil brother Xeleth orchestrated the attack on Toril even though the elves usually harvest uninhabited planets (true, kind of- they were in on it together)

• Xeleth commanded her to be dropped on Toril so that she would be destroyed by the astral blight but the ship was boarded by vampirates and she was captured (true)

• She wants vengeance (true) and will do her best to save toril if the characters help her become empress (false)

• the only way to stop the energy harvest is by destroying the energy harvesting device at the top of the temple of light on the Citadel, which orbits Xaryxis (false- the device is just a decoy at this point, the set of rings belonging to the twins are the real harvesting devices)

This sets up Xedalli as a wolf-in-sheep's-clothing ally to the party, and they agreed to help her, believing that she could set the Xaryxian Empire back on a peaceful path and save their planet. I also think there's nothing more fun than a good final act NPC betrayal, and this worked out pretty well.

This is how it ended up playing out:

characters arrive in doomspace to search for the coalition.

They find Warwyck Blastimoff, who has not been able to form a coalition. the factions in doomspace don’t see the empire as a threat.

Characters seek out Vocath to convince the factions to join together. He wants them to fight in an arena in exchange for an audience with all the factions.

At the end of the fight, three Xaryxian star moths attack and try to kidnap Xedalli. The factions must all fight together to survive and win the battle. Xedalli is not captured. With that, the factions can be convinced that the empire is a threat. Whatever factions can be convinced, will join the coalition and lend their ships to the fleet. Note- I did not have prince Xeleth present for this fight, only a representative of the Empire.

The players plan an attack on the Citadel. NPCs from earlier in the adventure travel out to join the fight if informed. The fleet takes on Xaryxis’ forces while PC’s ship infiltrates their defences using Gargenhale's invisibility spell and reaches the Temple of Light.

Xedalli and PCs battle Xeleth at the Temple of Light and attempt to destroy the harvesting device (which, unbeknownst to anyone, is pretty much inert and breaking it does nothing), while the coalition fleet battles the Xaryxian forces outside. In the temple, a projection of Toril shows the planet dying in real time, crystal vines choking the surface and motes of energy concentrating in a beam toward Xaryxis. The climactic moment: Xeleth lays dying, a final blow is dealt to the device, and… nothing happens. The vines still grow and energy motes still gather. PCs turn to see Xedalli taking the twin Ring of Shooting Stars from Xeleth’s finger, and she performs a fusion spell that turns two rings into one, concentrating the diverted energy into herself, healing herself to full, surrounding herself with motes of Toril’s energy. And then I wrote a whole evil monologue revealing that this was her plan all along.

Phase 2 boss fight with powered-up Xedalli! My players have a crazy ability to blow through 'deadly' combat encounters with ease, so I gave Xedalli some extra powers, including hp replenishing at the start of every turn from her ring. The party can only kill her and save their planet by destroying her fused ring. Once they do, the crystal vines on Toril wither and die.

This leaves the Xaryxian Empire intact but without leadership, and players can convince the priests or whoever else has some authority to go back to their more peaceful methods and never again try to harvest a living planet.

The party consists of the tabaxi Barbarian Tabasco, her brother the Tabaxi Fighter Ghost, the small sick Luma (pigeon) cleric Aurelius Lumestra, the tiny Jerbeen (squirrel) cleric of the Night Astar, the Raptor Ranger mailman Merlin and the stoic stone golem (goliath) Artificer Bard Stolz Felsenhauer.