meleebrawler
Smash Hero
Pac-Man fought against Spooky in Pac-Man World 2, a ghost that makes other ghosts tremble in fear.That's actually a fairly active thread even today, and I was actually the main person speaking for Rosalina being canonically the most powerful Smash character, tied with Shulk.
Reception to the theory was mixed but more on the supportive side (and I posted my list to tumblr and it got support there too).
The discussion has moved on from Rosalina for a while now, currently seems to be focusing on Sonic (who I have also been speaking in defense of but I'm kinda giving it a break because it's getting tedious and I just want Smash to come out).
To summarise the discussion, people argued that Rosalina can't actually be that powerful if she needed Mario's help in Galaxy, but I argued that this is blatant "gameplay-story segregation", since Rosalina, even with just her demonstrated powers in Galaxy 1 alone being taken into consideration, demonstrates that she would be perfectly capable of handling Bowser with ease, and could definitely collect all of the Power Stars (and 3D World backs up that she can go on a platforming adventure even using her most basic abilities). And Bowser raids the Mushroom Kingdom no problem with his huge fleet, yet had to resort to absorbing the Comet Observatory's power from a great distance, and despite the Observatory's small size and lack of turret defenses or anything of the sort, Bowser doesn't dare touch it. Why? Well Rosalina's there, of course. Rosalina is just as much a victim of gameplay-story segregation as Peach always has been, which is a shame, but it should NOT be used to say she ISN'T powerful, because it means nothing. Canonically, in cutscenes and such, the powers Rosalina has are immense, way more than even Bowser could hope to achieve.
People also argued that the universe's rebirth was not Rosalina's doing (it's commonly accepted that it is her doing), and that she said it was the Lumas doing it, but she never said this, she merely said they would be reborn, much like almost everything else. Also, trying to assume Rosalina was not the person handling this process opens some gaping plotholes in the Galaxy lore, many of which pertain to Rosalina's own existence being a huge contradiction under this assumption, and nobody could/can come up with ways to make it seem otherwise. That's why the implication is obviously that it is her doing.
Rosalina is generally just one of the most misunderstood and misinterpreted characters I know, a lot of people miss very obvious details about her and it baffles me as to why.
Here's the topic:
http://smashboards.com/threads/whos-canonically-the-strongest-character-in-smash.347421/
And here's my most up to date version of my list (only did Smash 4 characters though):
SSS:
SS:
S:
A:
B:
C:
X:
Just as an FYI, characters a tier below another character does have a chance against the higher tier character if they were fighting, but they would likely require some extra help in the form of power-ups. Or just dumb luck.
X Tier represents "Unranked" characters.
These guys are unranked because they are all docile in their source games as far as I am aware.
These two are unranked because I simply do not know enough about them to judge.
Well to be fair, I can't speak for many of the characters there myself.
Mega Man should definitely be higher though. I can't see him being any lower than mid tier. I doubt he will become top tier, but he's still really solid. He has a very poor match-up against Rosalina, though.
(Though he did need golden fruit power-ups to fight him...)