After the civil war in Lex's Legion between Tina Greer and Mikail Mxyzptlk, Mxyzptlk was forced into hiding. Eventually he was able to build up his forces again, and he was also able to plant spies within the Legion and the Justice League.
Mxyzptlk learned from his spies in the Justice League that the League was planning to attack a Luthorcorp installation which housed a weapon that could be used to kill a Green Lantern in orbit.
From the information he gathered from his spies in the Legion, Mxyzptlk determined that the Justice League would fail, even with help from Kyle Tippet and Chloe Sullivan, both of whom had all of Clark Kent's powers.
Mxyzptlk sighed. Although his forces were sizeable, he was still no match for the Legion. He had counted on the Justice League to weaken the Legion enough so that he could finish them off by himself.
Mxyzptlk decided that if he couldn't have victory he would settle for revenge. Together with help from