That battle was bs though.

Kratos is the most violent, angry and powerful character in pretty much all video games. (See how he um... dealt with the Furies at the very end... major anger issues... um yeah.) Anyway, if somehow you can come up with a scenario where the entire SSB team is able to take Kratos.... who by the way obtained the ability to reverse time in Acension (yeah, this is what the Smash Bros are dealing with here) they will be far too exhausted to take the rest of PAS and Cole and Evil Cole would clean up who are immune to PIkachu. Jax, Drake, Ratchet, Dante and the boy from Killzone would lay down a barrage of oppressive fire that would kill anything else and and Fat Princess would eat Gigglypuff. Game Set and Match.

Folks have eaten Kratos in the past... it didn't work out for them very well... (See Kronos death)

Yes but since we are obviously taking these characters from their most powerful states and pitting them against each other, Shulk is pretty much impossible to beat at his most powerful point.  To the best of our knowledge, he is omnipotent at his highest point, having been given the power of the True Monado, the power to destroy and recreate the universe at will.  Defeating him at that highest point is, from all practical points, impossible. 

Not really sure.  Kratos killed Zeus after willing himself back to life.  Doesn't really matter how many times Shulk destorys the Universe if Kratos can will himself back.  Also, being able to freeze/reverse time really nulifies anything Shulk does... unless Shulk exists outside of time itself in which case it doesn't really matter because doing so would mean Shulk doesn't exist... (a common paradox/pitfall built into omnipotence) lol.  

Samus would screw attack Kratos to death. He can never get near her thanks to the speed booster and shinespark anyway. Her range of fire is far is far greater as well.

And if he's up against phazon samus he's dead or corrupted after one shot. Plus she's litterally invincible in hyper mode. She can even drain his life energy. Or pump so much phazon into him that he explodes.

For some reason I thought you were talking about something else

Willing yourself back to life is not the same as willing yourself from non-existence.  Also, the definition of omnipotence kinda screws Kratos, especially given that in his world gods obviously aren't omnipotent and he is one of the gods of that universe, just like Zeus, and thus subject to the same principle limitations.   

Also, as a side note, existing outside time - or rather, existing in such a state in which time is a freely traversable dimension such as height and depth - doesn't nullify existence.  If you were to perceive the world as a cube, for example, someone existing "outside" or "above" time would perceive the world as a tesseract.  To use a rough analogy.  Rather than seeing the verticle slice of existence that is the present, one would see the entirety of time at once.  Not that that has any bearing on any of this.  Alvis is the only one in Xenoblade with that level of existence and if you fight him, you. are. screwed.

Why?

Buu is super fast and can destroy galaxies.

As for Kirby, ever played one of his games? He's super slow and weak.