All right. Mario and Shiek... Here goes...
MARIO
Disclaimer: I know very little about Mario's metagame. I am basing this primarily on his moveset.
Mario's an odd character. He has no glaring disadvantages, other than his lack of obvious advantages. And vice versa...
Anyway, in the air, Mario and Falcon match up like so:
Nair:
Falcon: two hits, one very weak, the other a bit stronger than ftilt.
Mario: Sex kick, comes out very fast. Also, quite powerful at the beginning.
Fair:
Falcon: The Knee. Has some startup lag, also has some properties of sex kick.
Mario: Sweeping downward punch. Can spike. Has more startup lag than the Knee.
Bair:
Falcon: Backhand. Has a little startup lag, sweetspots at his fist. Can kill if saved.
Mario: Very fast backwards kick. Medium knockback, but is very useful when edgeguarding.
Dair:
Falcon: Stomp. Can spike or launch, depending on the hitbox. Can kill.
Mario: multi-hit spin attack. Decent damage, good priority.
Uair:
Falcon: Backflip kick. Large area hit. Spammable. Can kill if saved, but it's never saved.
Mario: Backflip kick. Faster than Falcon's, but smaller. Also has less varied kknockback.
All in all, I think Falcon has a better airgame, but Mario's can still destroy you if he's aggressive enough, thanks to it's speed.
Groundgame... Falcon has better range, but mario wins in the priority department. Knockback... Falcon has slightly more, I think. Not sure.
Damage... No idea.
Edgeguarding:
Falcon: Decent spiking ability, if he gets the chance. Can also stagespike with Bair.
Mario: Has the ****ing cape. Has a spike, can also stagespike with Bair.
All in all, most of what Falcon can do, Mario can do better. Falcon is better at killing, though. I think...
40/60 Mario's favor?
I might come back for a Shiek analysis. But, for now, there is work to be done.