Spawn of theiral Nebula (G-BT03/087EN) [Sovereign Star Dragon]

[AUTO]:Forerunner (When a unit of the same clan rides this unit, you may call this unit to (RC)) [ACT](RC) Generation Break 1 (This ability is active if you have one or more face up G units in total on your (VC) or G zone):[Put this unit into soul & Choose another of your rear-guards, and lock it] Choose one of your opponent's rear-guards, and lock it. (The locked card is turned face down, and cannot do anything. It turns face up at the end of the owner's turn.)