I made a Small two-shot campaign
The Shadow of the Mountain
* The Journey: The session opens with the players on a caravan; they are on an escort duty to protect it in the harsh blizzard.
* The Obstacle: An avalanche has caused the path to become blocked. The players may make an Athletics check (DC 12) to attempt to dig through it or Nature (DC 12) to search for a path that the caravan can use to avoid it.
Ice Mephits (CR 1/2): 3 Ice Mephits attack from the avalanche as the players attempt to dig through. If the players avoid the avalanche, the ice mephits attack them on the road
* The First Sign: On their way to Frosthaven, the players find one of the other caravans, however, it is stripped of all metal (The skulker has stolen it, don’t tell the party this)
* The Night Camp: Because of the blizzard, the caravan is forced to stop since the horses are freezing.
* The Siege: The Skulker prefers to stalk the perimeter of the camp instead of attacking. Use a grapple instead of a deadly attack for any combat here
* The Mimicry: The Skulker can mimic any noise it has heard before. It uses this to lure out players.
* The Skirmish: If the lure succeeds, the Skulker will surprise the players and begin combat, if it doesn’t, then the Skulker will attack the camp losing the suprise attack
* Arrival at Frosthaven: Just at sunrise, the players arrive at Frosthaven finding it coated in a thick layer of snow and ice. The players will be greeted by Kael, a temple worker who was working in the temple atop the mountain. Kael had cut out his own tongue to stay silent, as the Skulker is blind and only navigates through sound. (In the next session, the players will discover Kael is responsible for accidentally breaking the sunheart).
* The Mayor's Pleading: The mayor of frosthaven is a cheery halfling named “Harvey Hobblefoot”. He begs the players to climb the legendary mount frost, and fix the Sunheart, a magical artefact keeping the blizzards away and “The shadow of the mountain” sealed. Harvey will not explain more about the shadow, as he has never met it. The only living people to have encountered it are the players and Kael.
* If needed, this session can be extended by added a section of forest with combat against starved wolves (for a lower challenge)
SESSION 2: THE APEX OF SILENCE
Goal: Climb the "Dead Zone," navigate the Temple, and seal the Unravelled One.
* The Vertical Ascent: This is primarily an exploration session.
* The Dead Zone: This is a 500-foot vertical climb. Every hundred feet, the players need to make skill checks to climb, these checks can be of any variety if it makes sense to the DM. Any failed check, that would result in a fall, will cause the player to fall, taking slight damage and potentially dropping an item other than an important quest item. Other players can help them (e.g. catching them) to negate the effects of this dangerous fall at the cost of their next turn to climb.
The Dead Zone
100ft – Regular climb
200ft – Frozen waterfall, slightly harder climb
250ft - * The Mid-Point Nest: The players will come across a cave on their way up containing the stolen metal from Session 1. The Skulker has created a nest from metal objects, and lying within, they will find the Shield of Reflection and the tuning fork, important items.
300ft – Strong winds, Players must make extra checks to avoid the wind
400ft – Thin air, constitution saving throw, on a failure, Players take cold damage or a level of exhaustion
500ft – Summit
* The Temple: The temple is a dungeon filled with puzzles before reaching the Sunhearts Chamber
* The sound puzzle: A hallway filled with statues of screaming monks, blocking the door on the other end of the corridor is a large, glowing crystal. The only way to destroy this crystal is to strike the tuning fork. When the crystal is struck, the attacker takes 1d4 thunder damage and the tuning fork subtly vibrates.
* The light puzzle: from a crack in the ceiling, a concentrated beam of moonlight sines onto the centre of the room. This doorway is also blocked by a large crystal. When the light is reflected from the Shield of Reflection onto the crystal, the crystal shatters
*The weight puzzle: There is a large pile of heavily rusted armour in one corner of the room. Nearby, there is a pressure plate. The gate will only open if something that isn’t metal or wearing metal is on top. Between the gate and the pressure plate is a long stretch of thin ice, if wearing metal, the players will fall through into the gap and take slight damage. The players can throw armour to the other side; however, metal armour is a liability in the fight against the unravelled one
* The Hall of Records: Murals in this room will depict a history of the Skulker, detailing it is "The Mountains Shadow," and that it cannot be truly killed because it is not alive, it is merely an aspect of the environment.
Combat – 2 Shadows (CR 1/2): In the Hall of Records
* The Frozen Gears: This room will house an artifact, partially encased in ice within a giant machine. The players will need to unfreeze the artifact using fire or other ingenious mechanisms. While working on the gears, they will hear the Skulker scratching on the ceiling. The artifact will be placed in the centre of the room and will only become functional once the gears are defrosted.
* The Silence: When the final gears have been defrosted, the blizzard will suddenly cease and the Skulker will emerge from a crevice.
* The Shatter Mechanic: This fight is designed around using the Shield of Reflection to bounce the Sunheart's light onto the Skulker, forcing it to split into Echoes or Shards
Combat: In the Frozen Gears room, 2 Ice Spiders (CR 1) have spun webs across the machinery.
* The Containment: The players are not simply meant to hit the shattered fragments but are intended to use the Tuning Fork to "lure" all four fragments into the caged corners of the room simultaneously to activate the seal. The caged corners of the room should have been described and alluded to within the Hall of Records, with a book detailing their purpose and that any shards trapped within them will become solidified and permanent. Once the four fragments are trapped, the Sunheart's light will strike them and solidifying them into a solid shard of obsidian like material.
* The Epilogue: After the Unravelled One has been sealed, the Sunheart can once again shine on the valley. The caravan members will present a large feast in celebration of the town's salvation.