I cannot consistently beat Bowser at level 8 or 9 with ANY character.
Played against a level nine as Mario, it went down like this:
Dashing A > (turn around) Dashing A > (turn around) Dashing A > U-Tilt > U-Tilt > U-Tilt > U-Tilt > Short-hopped D-Air > Short-hopped N-Air > Money
Tried to take the dude on with Link, here's how King Koopa ended up:
Dashing A > U-Tilt > Short-hopped B-Air > (turn around) Boomerang thrown low > Short-hopped F-Air
And with Ike:
Back Throw > Back Throw > Back Throw > Back Throw > Back Throw > Back Throw > Sakurai cries in his sleep
Don't even start me on how Weegee handled it. But, in all seriousness, my roommate mains Bowser, has his chasing and Down-Special cancelling figured out, and I find that Bowser, while much faster, stronger, and effective overall, can still be combo'd properly, just how he used to be. Which is fine.