In the mirror universe, the IKS Negh'Var was the flagship of the Klingon-Cardassian Alliance during the 2370s. The Negh'Var was a Negh'Var-class ship equipped with a tractor beam. While under the command of the Regent of the Klingon Empire, the ship is also referred to as Regency 1. (Star Trek CCG; WizKids module: Tactics) She was much larger than her prime universe counterparts, as much as two times larger. While boasting fearsome firepower, her size made her somewhat cumbersome, especially when engaging smaller, more nimble starships and fighters.
In 2372, Regent Worf commanded the Negh'Var on an assault on Terok Nor. However, the attack was thwarted by the mirror Defiant, with Benjamin Sisko commanding it. With Sisko taking advantage of the Defiant's superior speed and agility, the Negh'Var was unable to defeat the rebel ship and was badly damaged, forcing Worf to order the flagship to retreat. (DS9 episode: "Shattered Mirror"; WizKids module: Tactics)
In 2375, the Negh'Var was equipped with a cloaking device stolen from Martok in the primary universe. Rom sabotaged the ship when installing the device, and the Negh'Var was easily overtaken by the Defiant. (DS9 episode: "The Emperor's New Cloak")
The Negh'Var was returned or recaptured by the Alliance at some point later in the year, when command was transferred to General Duras. Intendant Ro Laren used the Negh'Var as her flagship, though she repeatedly asked Legate Dukat for a Cardassian ship to transfer her flag to. The Negh'Var would later be returned to the command of Intendant Kira Nerys in the wake of the Terran defeat at Empok Nor and the exposing of Ro's treason to the Alliance. (DS9 - Mirror Universe novel: Saturn's Children)
After combating the USS Defiant from the primary universe, the back half of the ship blew apart and the front-end was veering out of control toward the Denorios Belt's charged plasma fields. (DS9 novel: The Soul Key)