Campaign Pitch: Dungeons Fall From the Sky, So We Delve Them

A historical account of events on Lillette A, a .85 PHI planet at 5.133 AU around Kelson 3 (stellar ref code 7833900). 

Timeline (local solar years prior to present)

• ~600,000Y: A Hivonium separatist seed-ship visits the Kelson 3 system, using illegal stochastic course-charting techniques to evade estimated pursuits. The seed-ship identifies Lillette A as the local biome most likely to support life, and distributes its payload, in direct violation of galactic propagation law.
• 110,127Y: The third in a series of sequential-path Persioxes probes passes within 16 lightyears of Kelson 3 and pings the system, calculating a 44% likelihood of an unauthorized biome. The results are relayed up the command chain for further action.
• 7088Y: Several Persioxes probes, traveling on altered courses in response to the first signal, provide triangulated scans estimating a 93% chance of an unauthorized biome. Kelson is listed for investigation, confirmation, analysis, and potential sterilization.
• 914Y: Crake, an Approxiare-class vessel, arrives at the system and establishes system perimeter control. 
• 897Y: Direct analysis across all seven Herber-Tavo categories confirms Lillette’s status as an illegal biome, with estimates suggesting over four million macroscopic species. The unusually fast evolutionary process is typical of Hivonium technology.
• 896Y: Given the speed of biome development, the crew of the Crake has no time to refer Lillette’s status back up the command chain for consensus. The crew, empowered to act on their own prerogative, vote 145.2-117.7 to sterilize the Kelson system of all life (fractions in the sum reflect the votes of clones that had not yet reached their majority, typical of ship votes from that period). The vote is unusually close, but a simple majority still prevails. System fabs are deployed and begin exponential production expansion.
• 781Y: The orbital shell is completed. The crew begins the three-stage process of recording extensive evidence of the biome, collecting samples of all unique life, and sterilizing the planet (informally, “flag, bag, and slag”).
• 531Y: The project timeline undergoes the first of dozens of extensions. Multiple proposals to either stop or delay sterilization are proposed. Revotes on the fundamental question are vetoed by Gecko, the ship AI, but disagreement among the crew inevitably slows work and spreads dissensus.
• 153Y: A severe GCR burst from outside the Kelson system hits the Crake, the orbital shell, and most of the system fabs; only a few inner-system fabs incidentally protected by Kelson’s magnetosphere are spared. Gecko institutes a red-3 alert (informally, a “Deep Ugly”) and takes priority on all systems it can still ping in the orbital belt. A deep-cover Hivonium virus, programmed to surface only in very high states of system distress, bootstraps itself into several of the most vulnerable fabs, then jumps to the orbital shell. Gecko, while attempting to quarantine the virus, descends into a runaway persona-splinter cascade. Soon over 2000 variations of Gecko are struggling for control of the orbital shell. Other Gecko splinters take control of individual fabs and quarantine them.
• 43Y: The crew aboard the Crake attempt to leave the system, but a combination of  internal dissensus, malfunctioning Geckos, and viral meddling cripples the ship in the outer reaches of the system.
• 28Y: Surviving crew aboard the orbital shell begin to abandon sections compromised by these events, desperately fleeing to Lillette’s surface.
• 0Y: A 263,000 m² chunk of the orbital shell in terminal orbital decay enters the atmosphere and streaks across the sky. Automated systems and the fragmented consciousness of the local Gecko splinter divert most remaining energy to easing the fragment’s descent, ensuring it is relatively intact as it gouges a deep ravine in a mostly unpopulated coastal region on the second-largest continent. Local feudal sapient populations immediately dispatch forces to investigate.

Dungeon is actually SPACESHIP and magic is sometimes TECHNOLOGY has a long and rich history in D&D, from Metamorphosis Alpha and Barrier Peaks all the way up to modern examples that I will not name, just so that I don't inadvertently spoil them here.

This scenario is obviously in the same vein. The principal changes are as follows:

• Instead of a long-ago secret, the arrival of space technology is a currently unfolding situation.
• Instead of something buried, hidden, and forgotten, the sci-fi aspects are obvious, unmistakable, and world-changing. 
• The arrival of sci-fi tech has direct geopolitical impacts on the world; factions and fronts care about these things.
• Humans are the aliens; the “elves,” “dwarves,” and so forth are mutations or random evolutions from human stock, but they are to their knowledge the "normal" residents of their world.

Up in space, we have a Deepness in the Sky / Children of Time / Children of Ruin situation. Down on the planet, the vibe is more like Troika or Anomalous Subsurface Environment.

Humans are aliens, but the natives of Lillette probably don’t find them naturally suspicious, once they are separated from their technology. The fantasy species on the planet may be intentionally designed, or the product of randomness, or some of both. An “elf” living on a particular part of Lillette will be accustomed to meeting sapient bipeds (“humanoids” or whatnot) who vary in relatively small ways. A “dwarf,” a “goblin,” and other such creatures are much more similar to an elf than they are different. A “human” would just seem like another variation on a common template. The now-stranded humans, on the other hand, are absolutely freaking out about all of this. But for the denizens of this fantasy world, this is a Tuesday. The humans are a bit like vault dwellers in Fallout; better tech, but lacking in survival skills.

The action of the game is driven by competition for the falling bits of tech. These are dungeons populated with weird tech, escaped experiments, hostile security systems, insane Gecko shards, the desperate surviving human crew members, and virus-corrupted robots. The local flora and fauna would also be weird and dangerous, and interact in unpredictable ways with the falling tech (add Scavenger’s Reign as an influence here too). 

There are a lot of threads for adventurers to pull on, in addition to delving dungeons and negotiating the factions:

1. Functioning Gecko shards that still want to raze the planet of all life.
2. Former crew now trapped on the planet who are aware of that plan and don’t want it to happen (at least, not until after they can escape).
3. Surviving crew still ensconced in functional sections of the orbital shell or the further-out system fabs, who are rotating through stasis, waiting for an opportunity to escape the system.
4. Maddended Gecko shards that have made contact with the planet and that natives perceive as “new gods” who have come to shake up the existing pantheon.
5. For advanced play, traveling to space is a possibility. It could be possible to explore the sections of the orbital shell still in orbit; the damaged Crake; and even the few fabs that remained functional.