It's a nice idea for a game, but It's not what I would call a mini-game, more like a small platform game.
Anyway,
One thing I noticed from the start was that when you got hit by a goomba and died, it was quite sudden. It would help if you had some kind of death "animation" when you get killed(Like then normal fall up and down trough the ground)
Getting into tight spaces was kind of hard. At the start i kept trying to get into the first small hole with four blocks after getting bounces back out by the last block, and just could not get back in, so I had to restart the game before it let me get in again.
Shell power ups was nice too, I have only seen the red once so far, but I will play some more later and find out other(I heard something about a golden shell power up)
Getting the red shell was kinda nice, because the shell slowing down was getting kind of tiresome, but the red shell power up fixed that =)
Oh, and one last thing i noticed, one life? get us some more tries before restarting the game, and I would find it MUCH more interesting trying to get further

Anyway, so far it looks like a good "mini"-game, the graphics seems to be from one game, and not a collection of different graphic types.
The music sounds good(Not too high, or low), and the sounds fit in nicely. The looping music sounds a bit off when restarting the music, but that's not a big issue.
Good luck on the competition

*Long post ftw. :P *