This page contains information regarding Star Trek: Discovery, and thus may contain spoilers.
Much larger than a Federation Crossfield-class starship, the Viridian was "armed to the teeth" with numerous photon torpedo launchers and protected by powerful deflector shields, as well as a cloaking device. It also possessed mechanical tentacles that could be deployed to physically grapple other ships, and a hangar bay large enough to accomodate a Crossfield-class starship. The bay was equipped with an array of antiproton cannons.
In 3189, the Viridian traveled to Kwejian, whereupon Osyraa demanded that the inhabitants turn Cleveland Booker over to her. When she was rebuffed by both the natives and Captain Saru of the USS Discovery, she began bombarding the surface with photon torpedoes before the Viridian was damaged by Booker's ship and forced to retreat. (DIS: "The Sanctuary")
Later that year, Osyraa tracked Discovery to the Verubin Nebula through a transwarp conduit, disguised to register as as a Federation ship on sensors. Upon reaching Discovery, the Federation ship cloaked and Osyraa followed suit, though both cloaks failed following a disturbance from Theta Zeta that disrupted the ships' dilithium stores. When Discovery attempted to spore-jump to safety at Federation Headquarters, Osyraa and a group of regulators transported aboard and captured the starship while the Viridian deployed its tentacles to forcibly subdue Discovery. The two ships, now one, jumped away. (DIS: "Su'Kal")
Osyraa subsequently used the Viridian to "chase" Discovery to Federation Headquarters, correctly predicting that Fleet Admiral Vance would briefly open the deflector shields to allow the Federation starship inside, not knowing that it had been captured. The Viridian then held position outside the shield while Osyraa and Vance conducted negotiations. (DIS: "There Is A Tide...")
Negotiations eventually fell apart and the two starships fled the station on course for Base 755. When Discovery's starboard nacelle was sabotaged by Lieutenant Owosekun, Viridian dropped out of warp and towed the vessel into its hangar bay. After Discovery's senior officers re-took the starship and killed Osyraa, the Viridian's internal weapons opened fire, but Discovery ejected its warp core and detonated it moments after spore-jumping away, finally destroying the flagship. (DIS: "That Hope Is You, Part 2")