Agreed.
Played that game too 100% so many times.
So I give out some tips!
The Arena: Kirby's stats don't change based on ability. He's nice and rounded all the way, but the partners does.
A CPU is really agressive and reckless, so it's a good idea to give it something that'll take a beating. In this case, I suggest Blade Knight (sword).
1v1 against meta knight usually comes to a draw. So you know he's good.
if it's a player controlling it, go with what's comfortable. Ninja for second player is sick if you're a master button masher.
Now for the song. Not amazing samples, but it sounds very close to the original. Sounds like you used sheet music for this. The pan flute sound is a little wonky to me, maybe try tweaking it? Raise the drums a level on the thingy. It sounds a little rattly. *shrug*
I think that's the timpani, so yeah. Just raise it a bit higher and it'll sound better.