The first and probably more fun, it is the Death Star at skirmiss battles. As you can see, it is a huge station with a huge new 3D model adding even turbolaser turrets in its surface.
This huge "thing" can not be spawned in a battle as other units because it is so big. By this reason, the unique option was spawn it with a ability but I want a fun thing. Now Tarkin with its ISD named Allecto will release the unit in the battlefield and it will translate his command to the Death Star.
It will be a expensive feature but clearly one very poweful because the new Death Star can resist more damage than most of the units.
Other feature from the new Death Star is how it loses the ability to destroy planets but the enemy units as fighters will be fligh around it and not inside it as it happened before.
It will not be the unique Super Station at skirmiss because there will be two more.;)