Mister Oz

Mister Oz is a major character in DC Rebirth and was for some time one of the main antagonists of the saga, however he has been surpassed in that field by his mysterious "benefactor", who was actually responsible for Mister Oz's descent into misanthropy and madness (this "benefactor" is none other than the crisis-wide villain, Doctor Manhattan, best known for his role in Watchmen).

Abilities
Mister Oz was vastly powerful, with alien technologies beyond anything seen in the mainstream DC universe - he was able to spirit away entities such as Doomday, Mister Mxyzptlk and Robin, confining them to prisons while keeping them exiled from mainstream events : he was able to monitor all of human history via massive monitors and could appear almost anywhere at any time.

Mister Oz could also fire beams of green kryptonite from his eye, despite such radiation being lethal to his people - he was reliant on his staff to perform these godlike powers, when Superman broke his staff Mister Oz immediatedly began to die but also seemed to regain his original mind, warning Superman of a greater danger and expressing remorse.. he was no match for Manhattan, who effortlessly spirited him away despite Superman trying to save him.

Trivia

 * Mister Oz is unique among many of Superman's villains in that he was not driven by petty power or hatred, indeed he had many valid points about humanity's seeming tendency for self-destruction, furthermore he became extremely remorseful after his staff was broken - revealing that Manhattan was the true mastermind behind Oz's misanthropic crusade.