He departed from his role as an observer when Lex Luthor attempted to magically reconstitute Brainiac from the point in space where he and Darkseid had met their ends. Metron tried to warn Luthor that he didn't realize what he was doing, but Luthor went ahead anyway. Sure enough, it was Darkseid that Luthor ended up bringing back to life, and the despot immediately resumed his quest to destroy Superman and obtain the Anti-Life Equation.Despite having tried to stop him, Metron later agreed to take Luthor to the one thing that could pull Darkseid away from the devastation of Earth: the Anti-Life Equation itself. Metron warned Luthor that a human being may not have the capacity to survive an encounter with the Equation, but Luthor managed to retain his sanity and present his gift to Darkseid.
SUPERMAN: Apokolips Now
JLU: Alive & Destroyer