On batman vs Iron man, I have to say one thing people are not taking into account is brains always beats brawn. Batman probably wouldn't even confront Ironman directly, he'd likely go back to the bat cave and program a computer virus that would shut down Iron Man's armor leaving him a big fat target, or maybe lure iron man into the path of a big fat magnet.
On some of these other ones, an interesting fact about Ryu is when he was statted for the ultimate fighters combat system dragonpunch had the very silly ability to counter anything! So, ryu gets stabbed? Dragon punch! tank fires a missile? Dragon punch! some huge bad guy blows up the world, dragon punch! It amused lots of role players.
If we're just going from the games though, unless melina was waiting in the wings to dagger assassinate anyone who beat up her main squeeze baraka, I have to say I'd give it to Ryu, just on the basis that street fighter wise the only people stronger than ryu are Guki, Gukon, Orro and possibly Jen on the basis that he fought Guki to a stand still.
Raiden vs skywalker, I have to give it to raiden here, just because as witnessed by the end of Return of the jedi, Luke Skywalker is really! crap with lightning, and Raiden is a guy made out of lightning, plus I don't think it'd be hard for someone who can control electricity to counter a light saber pretty easily, I can see it now, Luke activates, raiden holds up a hand and vsssssst, the blade goes away, vssssd, vsssssd! it would be quite funny.
Darth Vader would have more chance, though it'd still be a struggle sinse he'd not be able to use lightning, or the choke!
On Mega man, technically Mega man is not a repploid. Repploids were a race of robots created after Mega man x a hundred years after Mega man, and like X they had the ability to think for themselves and feel emotions as humans, which original mega man doesn't.
Original Mega man therefore doesn't have a soul, however arguably x might, indeed in the Zero series you see that X vacates his body and uses it to seal a powerful destructive force called the dark elf, yet is still around in data form as a cyber elf (no I did not make cyber elves up, they occur in the zero games).
So, maybe cyber elf x is actually x's soul, I'm not sure, though it amusingly does look sort of like X as an angel 
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One I would like to see is the liquid metal T1000 vs magnito! one is formed of liquid metal and can reform himself, the other can manipulate metal!
I think it'd go with the terminator being bounced around like silly putty by magnito and yet magnito couldn't actually do him any damage, it'd be funny either way!
With our dreaming and singing, Ceaseless and sorrowless we! The glory about us clinging Of the glorious futures we see,
Our souls with high music ringing; O men! It must ever be
That we dwell in our dreaming and singing, A little apart from ye. (Arthur O'Shaughnessy 1873.)
