▁c ros so ver , ▁featuring ▁several ▁covers ▁of ▁existing ▁songs ▁along ▁with ▁two ▁original ▁numbers . ▁Similar ▁to ▁" In vas ion ! ", ▁the ▁c ros so ver ▁begins ▁at ▁the ▁end ▁of ▁the ▁Super g irl ▁episode ▁" Star - C ross ed " ▁and ▁primarily ▁takes ▁place ▁during ▁The ▁Flash ▁episode ▁" D uet ", ▁featuring ▁the ▁Music ▁Meister ▁as ▁the ▁ant agon ist ▁who ▁puts ▁both ▁The ▁Flash ▁and ▁Super g irl ▁in ▁a ▁shared ▁hall uc ination . ▁After ▁" In vas ion ! ", ▁G ug gen heim ▁felt ▁" If ▁there ' s ▁an ▁app et ite ▁for ▁it ▁from ▁the ▁fans ▁and ▁from ▁the ▁network ," ▁the ▁c ros so ver ▁next ▁year ▁could ▁be ▁" a ▁proper ▁four - part ▁c ros so ver ." ▁ ▁At ▁the ▁ 2 0 1 7 ▁Pale y fest ▁event , ▁Kreis berg ▁re iter ated ▁the ▁cre ative ▁team ' s ▁intention ▁to ▁do ▁a ▁full ▁four - way ▁c ros so ver ▁the ▁following ▁year . ▁At ▁San ▁Diego ▁Com ic ▁Con ▁ 2 0 1 7 , ▁it ▁was ▁confirmed ▁that ▁another ▁four - way ▁c ros so ver ▁would ▁take ▁place , ▁with ▁Super g irl ▁playing ▁a ▁larger ▁role ▁than ▁the ▁previous ▁season . ▁The ▁four - way ▁c ros so ver ▁event , ▁titled ▁" C ris is ▁on ▁Earth - X ", ▁took ▁place ▁on ▁November ▁ 2 7 ▁and ▁ 2 8 , ▁ 2 0 1 7