Frostfell

The Frostfell, or Elemental Plane of Ice, is one of many Planes of Existence in the Critical Role universe.

Notable locations
There was once a rift in the Frostweald leading to Frostfell, through which Errevon the Rimelord invaded Exandria in a war referred to as the Icelost Years.

History
Less than two years into Zan Tal'Dorei's reign as Sovereign, the white dragon Skysunder, acting as a scout helping Errevon find the weakest points between the planes, slipped through the tear in the Frostweald and saw that the realm was battered from the decades-long Scattered War.

A short time later, taking advantage of a celestial solstice, the tear was expanded into a large rift, instantly plunging the surrounding lands into a deep, icy winter. Errevon and an army of creatures from Frostfell, including frost giants and sentient blizzards, invaded through the rift. The Icelost Years ended when rift was ultimately sealed by a combination of forces from the Kingdom of Tal'Dorei, Syngorn, Kraghammer, and the Ashari. This event is celebrated yearly in Tal'Dorei as Winter's Crest.

At some point, Skysunder was defeated and sealed within the Frostfell.

Winter's Veil Crisis
Following the long and devastating Scattered War, Tal'Dorei was significantly weakened. The white dragon Skysunder, acting as Errevon's scout to find the weakest points between the planes, used an existing tear between planes located in what would later be named the Frostweald. She saw the battered and divided realm, and notified Errevon that it would be advantageous to strike. During a celestial solstice, the forces of the Frostfell did so, further opening the rift and invading the Material Plane with their forces of living blizzards and frost giants. During the Winter's Crest Festival of 809 PD in Westruun, a mysterious blue crystal was delivered to the town. The crystal suddenly detonated, freezing everyone except Vox Machina, who were protected by Abjurist Noja. In the crystal's place stood Skysunder, in the form of a pale, nude woman. She opened a portal to the Frostfell and leaped through, closely followed by Vox Machina. Skysunder revealed her true form as a white dragon, although she was weakened by her premature rebirth. The party managed to defeat her, with Pike Trickfoot landing the killing blow.