The locals claimed to have spotted a strange, serpentine creature terrorizing the edges of town, swooping in to steal livestock and spook the farmhands. It leaves no tracks, just massive, slick puddles of black ichor. Strange, calcified tendrils seem to grow wherever it's spotted. The spooked farmhands claim to hear a sound like dozens of charging horses, and a shrill, hollow shriek, but none were brave enough to leave their homes to peer at the beast.

The First Doom has come.

Ossein is meant to be a battle fought as a high-speed chase, with the players fighting on top of and within a monstrous train.

The colossus rides on a self-generated railway dubbed the Landspine, which it dynamically constructs in front of itself. The Landspine itself is a durable, calcified structure that lasts for a few days before crumbling away, allowing PCs to chase after it on their mounts even should it take to the skies. Even so, it uses its features to abduct and imprison the PCs, forcing them to fight on its terms. Trying to set a trap to board Ossein while it's in transit would make for a good Colossus Hunt adventure!

Ossein is a predatory colossus, preferring to hunt and consume livestock at night. It swoops in on the Landspine, leaving nothing but pools of its ichor wherever it hunts. Sightings make it akin to a ghost train, but ideally, it should be described as vague and alien as possible by superstitious, unreliable, and confused eyewitnesses. The PCs should be unaware of its resemblance to a train until they're about to fight it.

Encounter Guidance

Below, you'll find the stat blocks for Ossein. Because of the current layout of Freshcutgrass, the Ossein, The First Doom Adversary card has 1 HP and 6 Stress, whereas every other segment has variable HP and 1 Stress; for mechanical purposes, please track all stress usage on the Ossein, the First Doom card, and mark its HP only when it is defeated.

Ossein's original incarnation has 3 Abdomen segments, but they can be added or removed as you see fit. I suggest having as many Abdomen segments as you have players, minus one - that way there is always at least one extra player who can move between Abdomen segments.

Despite the encounter being presented as a high speed chase, the encounter is not built with any specific mounts in mind. It assumes that the PCs are going to be fighting on top of and inside Ossein. If a PC fails on a roll to climb an adjacent segment, they do not fall off, instead taking damage or marking a stress as a result of Ossein's precarious, dangerous structure dealing damage to them. If appropriate, they may also be transported to the least damaged Abdomen segment.

Tactics

Ossein's goal is to trap and isolate PCs within each of its Abdomen segments, forcing the PCs into disadvantageous positions. By strategically Occupying empty Abdomen segments, Ossein can keep heavy hitters away from its weak points. Choking Smog prevents flying PCs from ignoring their allies, and can even imperil them if they try to stay away. Should any solitary PCs make their way to the Rear, an Abdomen segment can use Abduction to reposition them away from the weak point. If at least one PC makes their way to the Head, you can Spend a Fear to respond with Eject Passenger; lucky PCs, or those built for navigation, can turn this feature around and move to the Rear.

Ossein is built to dismantle parties that don't cover for one another. Abduction deals catastrophic damage to single targets, but with 2 or more PCs working together, they can ideally take down an Abdomen before that becomes a problem. Private Car encourages the party to buddy up, or even jump in to allow their teammates to move to the Head or the Rear. By tactically destroying one abdomen at a time, the party can use Coupling to move together and make coordinated attacks on either the Head or Rear.

Ossein's Stress features are meant as a way to ensure that even uncoordinated parties can make it through if they can survive for long enough. Emergency Repairs lets Ossein recover unfocused, minor damage, hopefully encouraging PCs to focus their efforts on one car at a time. Eject Passenger is best used if there are two or more PCs on the Head - even better if the PCs manage to arrive on the head simultaneously thanks to the Rear's Weak Point feature. Make sure to restrain yourself, only using Eject Passenger when the PCs have at least attempted to deal damage, and ideally after Ossein has marked a Hit Point.