Greatest upsets in comics
Where a C lister/underpowered character who isn't Batman puts down someone wayyy above their weight class. Power level matters less here then "pecking order"..
I'm thinking the Rock of Ages story is up there, when future Roy Harper and Atom fry Darkseid's brain with a laser.
Also, in For the Man Who Has Everything, it was JASON TODD (When he was still a lame Dick Grayson clone) who defeated PC Superman stomping Mongul, by throwing the Black Mercy plant at him.