Dude, Mordru is one of the baddest arse in the DCU!
He has stolen the power of Dr. Fate (helm, cape and all)!
Before that, he stole the power of Arion, Archmage of Atlantis!
When he was after Kid Eternity (who could summon heroes - even superheroes - from the past to protect him), he killed Perseus, Pegasus, Hal Jordan and several others (who promptly returned to their timelines).
He has plagued the Justice Society in the present... AND the Legion of Superheroes in the 30th century (when magic is supposed to be dead)!