Oh.....but Dark Bowser was going to destroy the MK and statements in the game also support he was going to destroy the world, which is clearly larger than an island. Anyway, here's Mario's notable fights in franchise. I'll be including fights where he has nothing or no one argumenting his powers so most of the PM series as well as certian event fights such as his battle with Antasma will be excluded:
SM64: Against Bowser with the Power Stars. Bowser used the Power Stars to create worlds in the paintings and trap people in there. Truth to be said, I don't know how large the worlds are but some of them has a sun in it and we later learn what power stars are capable of in the SMG series if you wish to use this info.
SMG2: Fought Bowser again but this time with a Grand Star, an artifact Bowser was going to useto create galaxy and destroyed the universe in SMG1. He did nearly the same thing in the final battle via Black Hole.
SMRPG: Fought Smithy, who is superior to Exor. He also fought Culex. He doesn't receieve any notable power buff in his end from what I recall.
M and L:BIS: Fought the Dark Star and the Dark Star Core. The Dark Star in the past was only defeated by the Star Sprites, who are similar to the Star Spirits. He also beat Bowser in the credits, who just destroyed Dark Bowser.
M and L
T: Fought Dreamy Bowser who is basically holding the power of mutiple dream worlds. I want to say he also help Giant Luigi with the Zeekeeper but I believe the only time he can aided him in these battles is when they use the Drill Stomp attack.
PM: Color Splash: Fought Black Bowser. The black paint powering up Bowser is basically a mix of all the colors which according to one of the Big Paint Stars, gives life to the world.
M and L
J: Fought ShinyRoboBowser, who can counter Paper Mario's Trio Attack. One of the Trio Attacks involves Paper Mario reality warping them into a space arena with actual stars, unlike previous attacks.
As we all know, he also fights Bowser and his army regulary hence why I didn't mention most of the other games.