Visually distinguished from its predecessor by its distinct X-shaped outcroppings, the Victory-class Star Destroyer Mark II also incorporates a different design philosophy than the Mark I.
The Victory Mark II is meant more for space combat and as such loses the ability to operate in an atmosphere. The ship is faster and has more powerful guns than the Mark I, but sacrifices some of its shield strength in the process.
Unfortunately, since it came out after the conflict of the Clone Wars had ended, the Mark II wasn’t constructed in anywhere near the numbers of the Mark I. It isn’t quite as rare as its Kuat Drive Yards cousin, the Venator Mark II, but it doesn’t show up in Imperial fleets with the same regularity as the Victory Mark I.