Yamcha vs Superman, Arceus, Screampaste, Goku, Thor, Bills, Spawn, Naruto, Ichigo, Luffy, Galactus, Iceman, Deathstroke, Dr. Fate and the entire MK and SF verse and Docter Doom. This is how I would see it happen.
they all try to blitz him then Yamcha uses his awesome fail power to slip on a banana and fail at life they makes everybody laugh themselves to death so in my opinion Yamcha solos with his awesome fail power.
Yamcha regales them with some awesome, likely hilarious story that no one else could have told, illustrating this with the appropriate Yamcha pics. He will respond to everything said/done with same said pics.
After this goes on for a few minutes, the opposition concludes "Haha, this guy's f**king awesome! You're a trip, man! You should come live with us!"
Yamcha effortlessly befriends his opponents and solos the omniverse. /thread