In a hypothetical...
1. Scorpion is by no means immortal. I don't think there is anything historically that would support that.
2. Scorpion is not a demon. He is a human sent to the Netherrealm and later to hell.
3. If we're really going to do this we need to find a character akin to Scorpion in a comical universe. The two that come to mind are Spawn (not DCU) and Spectre.
3a. Spawn because of his ability to summon hellish powers.
3b. Specter because he is neither living or dead. He is in a state of oblivion. I don't think it is fair to call him a ghost.
4. We have to establish whether or not Scorpion's powers are mystical (magic) or ethereal (of the earth). If they are mystical or magic, we can almost completely throw out Superman.
4a. The trouble arguing a Superman fight would not be a matter of if Superman could/would kill Scorpion since Scorpion is neither living or dead. The trouble with a Superman argument is if Superman were able to actually kill, would he kill Scorpion (considering his moral philosophy).
4b. If Scorpion is somehow defeated by Superman, he would only return to the Netherrealm.
5. Scorpion was formerly a ninja so tactically he is versed in several weapons, has a strong tolerance for pain (if he even still feels pain), *possibly studied the teachings of Sun Tzu (Art of War) and is very capable of adapting to his surroundings.
5a. The Batman Family (for the most part) loses this match up not because of Scorpion being a ninja but because of all the extra stuff. If it is a FIGHT without all the extras edge is probably more in Batman's favor because he is well versed ninjutsu in addition to several other martial arts. They are even in almost everything even height and weight until we consider experience, adaptation and knowledge. Scorpion can win in the experience category but he may be out matched in knowledge and adaptation (maybe even intellect... still, Scorpion did lead an entire clan of ninjas). With all of that said, the Batman bunch loses because of the mythical qualities Scorpion possesses.
6. So, with all of that there are still several other considerations that could be made but I will conclude with this one... Since we are talking about a corrupted soul and a being neither living or dead we are dealing with a mystical being. Though the most similar character in the DC Universe is Spectre, here are a few more undead characters: Solomon Grundy, Black Lanterns and Deadman. THE KICKER in all of this is what or who can end what is neither living or dead, and if that thing were to challenge Scorpion would they be able to stop him before his assaulting them.
6a. That person has to have some knowledge of necromancy and the black and white arts.
Taking all of that in here are the character I believe could take out Scorpion (I nerded out too much so if you want a reason I'll give it later):
Spectre
Phantom Stranger
Madame Xanadu
Doctor Fate
Raven?
Black Alice?
I won't do it but I'm interested to see how the Lazarus Pit and the inclusion of the Sandman canon play into all of this.
