7. Imperiex Prime
Imperiex is made up of pure energy and utilizes a humanoid suit of armor in order to harness his energy. His one and only goal is to destroy the universe. In the Our Worlds at War arch it took most of the heroes and even some of the villains of the DC Universe in order to stop him. Imperiex previously destroyed Warworld, Mongul's home planet. Mongul then proceeded to ask Superman for help in stopping the all powerful Imperiex. Eventually he was neutralized but not destroyed as it turned out to be an Imperiex probe. His powers include super strength, durability and stamina. He also has the ability to shoot out energy beams and destroy all living things which he once used to kill Doomsday!
His Weakness? Being an energy source, he does require a physical shell of a body to store his energy. Which means that his shell of a body can be destroyed. Also, in the Our Worlds at War arch he was eventually consumed by Brainiac 13 and sent back to the beginning of time where he was destroyed by the forming of the universe. The fact that it took another villain to defeat him should tell you all that you need to know.