We know alto about the Justice League. But i thin knot as many know about Monster X.
Monster X is basically a super version of King Ghidorah. He's at par with other monsters from Toho such as Godzilla and Destroyah. Some of the most powerful monsters from Godzilla series. Monster X is roughly 120-140 meters tall and wights 60,000- 100,000 tons. He's summoned by the alien race, the Xilens to fight Godzilla while they try to execute their plans against Earth.
Monster X can travel at FTL, Mach speeds speeds as seen in Godzilla Final wars. He can leaviate which means he was physics powers. He can also fire beams from his eyes. He will turn into Gaizer Ghidorah when is being defeat. Thus making him even more powerful. He can also paralyze enemies using it's lighting bolts at Ghidorah form. At Ghidorah form, he's also able to suck the health from enemies and use gravity bolts.
Monster X is a very powerful monster. He was the only creature in almost all movies that survived multiple blasts and one too the face from Godzilla. His beams posses the same power as the ones from Godzilla. He's also a physical match for Godzilla and Destroyah.
Assuming his only weakness is seen in Godzilla: Final wars. Then i think Superman is going to die first. Keizer Ghidora (his super form) was only defeated when Godzilla powers were boosted to infinite. After that Godzilla delivered a final Super Blast which desintagrated Keizer Ghidorah.
Who will win this battle?