Gatshadow Mountain

 was an enormous, ominous mountain in Tal'Dorei at the southeastern tip of the Cliffkeep Mountains, just northwest of the Bramblewood Forest and Westruun. It got its name because it was dark and ominous with a dark, blackened rock peak that stood out amongst the rest of the mountains. While other mountains crest at 4,000 feet up, this one was over a mile high. Gatshadow's peak was nearly always obscured by storm clouds or mist. Most of the trees were dead or dried out towards the top, but other than that the vegetation was pretty sparse.

The actual stone that comprised this monstrous formation was of a darker, more dense stone and it was considered to be the finest stone for crafting on the Tal'Dorei continent, hence why many crafters and smiths made the dangerous journey there to quarry the rock—and not all return.

Entrance
Around the big cavern entrance there were clumps of dead, petrified trees. Leafless, gnarled, and devoid of any life. There were signs of melted stone and soot. Long ago, there may have been a fire that claimed the top of this mountain and set its visual presentation. This entrance was just an opening on the side of the mountain with no walkable path up to it. 60 feet below it to the left was another small entrance. 40 feet before this entrance there was a scaleable wall, at an upward angle.

Around the exterior of the entrance, there were two rocks embedded in the sides of the wall, about three to four foot in diameter that were nearly identical, placed at each side of the cavern entrance. Their texture and their weathered appearance was far younger than the rest of the stone around them.

Small Entrance
This hole continued for 15 feet into the mountain before it ended abruptly by a cave in. There were four long-dead skeleton corpses within this hole. Perhaps some sort of mountain-climbing expedition or travelers that found their way there, and couldn't escape. There were remnants of a small camp. Perhaps a small fire that was long iced-over through winters past. A layer of dust sat on everything and other than the occasional gust of wind that found its way in here, largely undisturbed for a long period of time. There were roughly 85 gold pieces amongst their corpses and spare change in silver and copper; an oil lantern; climbing gear for four people; some long-spoiled rations; and a very moldy diary.

Cavern
In the cavern there were pieces of stone jutting out of the floor, two pools of somewhat greenish-brackish pungent-smelling liquid. Next to one of the pools there was an elevated platform where a large outcropping of stone had just slowly pulled itself out of the rock, nearly touching the very height of this cavern. The ceiling had a height about 70 feet tall there were a few stalactites points of rock trough out this cavern.

There were portion of the mineral growth, and a lot of the moisture that had coalesced into the ceiling had come into a central point, and over time, it had built up central columns of rock and natural materials. A few pools had gathered towards the base. Portions of the ground had elements of the acrid liquid that filled the pool. The mineral build-up of the inside of this cavern led to a direct, slick surface in the walls, and rounded off most of the stone.

There was an additional pool of acid, at the far back corner and a risen platform, the portion of the cavernous stone began to mass into a higher level towards the far back corner.

History

 * In the Age of Arcanum the Gatshadow mountain was transformed in an evil place. As Acek Orattim, a priest of the Betrayer God the Chained Oblivion, made it his seat of power. The power of the Oblivion’s corrupted the mountain range to making this peak a jagged needle that towers over the rest of the mountains. After the banishing of the Chained Oblivion it was said that Acek’s mind and spirit were so filled with his masters essence that his body tore to asunder. Which left an empty maze of deadly chambers and traps behind beneath the mountain, forgotten and awaiting rediscovery.


 * There was once an expedition to reach the peak of Gatshadow, because there was some sort of movement, some sort of activity up there that nobody could really discern. The rumors spoke of some sort of creature that would stalk out in the night and steal mountain goats, or find and kill anybody who lived in the small village north on the mountainscape that was abandoned because of this creature the folklore of the time said supposedly lived at the top of the mountain.

Critical Role: Vox Machina Origins
Vox Machina journeyed to Gatshadow early in their adventures, delving into the mountain itself:

"''Weeks pass, and Grog the barbarian hasn't been seen since suddenly leaving for the city of Westruun. Heading there in search of him, the party meets his childhood friend—and their new companion—, the gnome cleric Pike. Grog apparently hasn't been acting normally and had marched off on his own through the Bramblewood towards the ominous mountain, Gatshadow. The party followed, dispensing with a troop of roadside thieves along the way, and wound their way toward the mountain. Deep within, they encountered an abandoned subterranean city and eventually a crypt housing a mind-controlled Grog, the reanimated corpse of his father, Strongjaw, and a dying mage attempting a ritual to lichdom. Our heroes slayed the mage, but not before he could complete the ritual and embed his phylactery into Grog's chest.''"


 * –excerpt from

Umbrasyl did not always live on Gatshadow, but made it his lair after the Chroma Conclave's attack on Emon.

After the Chroma Conclave attacked in Chapter 4, the ancient black dragon Umbrasyl roosted in a cave at Gatshadow's peak, receiving tribute from Westruun. Several scouting parties from the Herd of Storms were sent to Gatshadow in preparation for an attack on Umbrasyl, but they didn't return. Later, Shale and some other warriors from the herd scaled Gatshadow. Shale's age and disabilities slowed her down, so she survived Umbrasyl's slaughter of her party by a twist of fate, then descended from the mountain in time to meet Vox Machina. Together, Vox Machina and Shale ascended Gatshadow and slew Umbrasyl in his cave.