Tyrantfog

The Tyrantfog was a magical ritual, empowered by Iyachtu Xvim, that Fzoul Chembryl devised to save his own life. It struck down followers of Cyric across Faerûn and allowed Xvim to absorb the power of many Banite relics.

Location
The ritual itself took place at Zhentil Keep, and caused two massive clouds of gray fog spread across Faerûn. The first spread throughout the Moonsea and the Heartlands, reaching as far south as Starmantle, as far north as the Sunrise Mountains, and as far east as Tsurlagol. The second cloud arose around Mintar and spread northwest to Saradush. The ritual's effects affected much of the Western Heartlands, western Sea of Fallen Stars, and southeastern Tethyr.

History
In Alturiak of 1370 DR, the banelich Faram Khaldan decided to put into action his plan to assassinate Fzoul Chembryl. Using information given to him by Manshoon, Faram managed to get inside the underground temple of Xvim beneath Zhentil Keep where he encountered Fzoul. Fzoul, armed with the Scepter of the Sorcerer-Kings, plunged it into Faram's chest, which broke the artifact into five separate pieces that were then flung into the planes. Faram was destroyed but the magic released both destroyed the temple and filled Fzoul's body with a massive amount of magical energy.

Fzoul knew that the energy his body now contained would soon kill him so he began work on a ritual to expunge it, although the Manshoon Wars erupted soon after, delating him.

On Mirtul 3, from an altar in the ruined northern section of Zhentil Keep, Fzoul sacrificed many captured Cyricists and Zhents loyal to Manshoon to fuel his nine-day ritual. This had the effect of conjuring a dark grey fog that stretched from Zhentil Keep south to Starmantle and north to the Sunset Mountains, reaching as far east as Tsurlagol by Mirtul 9. A second area of fog appeared between Mirtul 8 and Mirtul 10 between Mintar and Saradush.

Xvimlar found strength within the fog, while Cyricists in the fog were afflicted with a terrible disease. The Knights of the Black Gauntlet used this new-found strength to conquer Kzelter.

On Mirtul 11, the fog burned away in a great green conflagration. All holy sites of Bane within this "Tyrantfire" lost their power, and holy sites of Cyric were incinerated along with many Cyricists who had thus far survived. All baneliches within the area of the fog were destroyed as well, destroying the majority of those then surviving in the Realms.

The green fires leaped into the sky before converging on Fzoul. Both he and Xvim were greatly empowered by the energies of the Tyrantfire.

After-effects
The Tyrantfire's flames became concentrated into a huge pillar of green and black fire over the altar where Fzoul began the ritual. He stood within the flames, unhurt, and released the stored energy within him. Though he did not burn, Fzoul still died once all of the magical energy within him was gone three days later. The massive amount of power released by the ritual was fed to Iyachtu Xvim, however, and in thanks, Xvim resurrected Fzoul as his Chosen a day afterward.

Upon Fzoul's resurrection, the pillar of fire was transformed into basalt and was quickly made into a grand temple called Tor Blackflame.

All Banite magic items in Myth Drannor were consumed by the Tyrantfire but the flames mysteriously coalesced into the form of a dragon before rejoining the diminishing radius of fire.

All those who succumbed to the diseases caused by the Tyrantfog rose after the Tyrantfire as tyrantfog zombies.

Xvim himself was greatly empowered by the ritual, laying the groundwork for Bane's return through him less than two years later.