The Fall 2019 DCTV crossover will be an adaption of DC Comics most famous crossover of all time - Crisis on Infinite Earths! Heroes will fall and the universe will never be the same. In the Supergirl Season 4 finale, The Monitor brings Ma'alefa'ak, the twin brother and arch-nemesis of Martian Manhunter, to Earth. Monitor then pays a visit to supervillain Lex Luthor.