Two variants are forced to merge using unholy magiks by The Enchantress to create the perfect vessel for a malevolent entity hellbent on preparing the Earth for a dark transition, an emergence one could say of the Elder Gods that was once worshipped long ago. Supergirl and Powergirl, their consciousness trapped in that "sunken place" forced to merely watch as they are used to enact utter destruction.
With Superman and other cosmically powered heroes dealing with an offworld threat, hope seems lost. Who will step up and put an end to this???