[quote=@ChickenTeriyaki]
Superman: [i]*Punches Aquaman into the sky*[/i]
[/quote]

Any number of super villains and Batman with Kryptonite puts Superman down.
Any number of magical super villains and heroes puts Superman down.
Any number of super villains and heroes with red sun generators, red sun grenades puts Superman down.

Firestorm can create Kyrptonite, DEO can create artificial Kryptonite.

There are numerous ways to knock Superman down a peg or two or outright kill him. If a player can't figure out how that proves they are not good enough to being playing.