DC cosmic history: c. 7000 BCE: Eclipso causes the Great Deluge to destroy human civilization. Xavier Nihilo, a common man, builds a boat to save his family, but Eclipso confronts him. Nihilo pleads for his life in return for his family's survival. Instead, Eclipso kills Nihilo's family and taunts Nihilo by making him immortal. Note: Nihilo states he is 9,000 years old.
Noah and his family are saved from Eclipso's wrath. When Noah sends a dove out to find evidence of land, Eclipso crushes the dove. The bird explodes into pure, white light and Eclipso's essence is then banished to the moon, while his body is transformed into the Heart of Darkness. (#1) (The dove was a ruse to trap Eclipso. ([#10]) Note: Placing Noah 9,000 years ago is not consistent with the timeframe established for him in the Torah, since the Jews believe the world is less than 7,000 years old.
4,000 BCE: Eclipso is banished to the dark side of the moon. His evil influence is held in the "Heart of Darkness" black diamond, created for that purpose.
He posses people basically. He has shown and inconsistent ability to take coporeal form. I doubt eclipso has the strength to keep someone with magneto's will power for long. Mags bansishes eclipso back to his rock, wraps it in 20 tons of junk and puts him into deep space. While magneto is making a dick like speech and feeding his ego, superman speedblitzes him for no reason other than he can. Magneto is a smear on the ground. Superman flies off. Superman is a dick.