The Shaitan’s Key open Lair of Shaitan dungeon.
The Lair of Shaitan is a high level dungeon consisting only of a boss fight. The dungeon is the source of the Skull of Endless Torment which was previously a long-unreleased item, and, since Release X.28.0 (July 2018), also drops the Wakizashi of Crossing Fires.
The Flame Cloth (Designed by WunderWafe) and the Heavy Chainmail Cloth are site-specific drops, and there is currently no other way to obtain them.
The dungeon is accessible via the Court of Oryx.