Your optimism is refreshing.
Seriously, there was an unnecessary Luigi code in NSMB. In fact, Nintendo has learned over the years that the fans love them some Luigi, even if he plays the same. This became obvious with more recent games like SM64DS, NSMB, and Galaxy. If they decided to nix this traditional Easter Egg (especially with the opportunity to pander to all the Toad fans as well) for this game, I'll be disappointed.
In the meantime, I got a few more hints for you all because I'm feeling generous.
Spoiler Below - Yoshi can slurp up other player's fireballs/iceballs and spit them out as floating projectiles.
- When playing multiplayer and faced with a throng of grounded enemies, you can take them all out with one decisive blow by pounding the ground simultaneously. Although this maneuver mimics the POW Block effect, it does not drop floating coins like the latter does.
- Items you can lift over your head provide protection from threats from above, as well as serving as a platform for other players.
- With cooperation, two players can reach great heights if one bounces on another's head while the latter jumps as well, trampolining the former further if he bounces off at the bottom player's apex of his jump. The maneuver becomes more effective adding more players into the mix, but requires more timing and patient teamwork.
- You can jump while sliding on your belly in the Penguin Suit, and resume your slide as you land. Just keep holding down that down button.
- You can share the power of the Starman by lifting other players. The time spent being invincible carries over, so don't count on trying to make it last forever through some glitch, 'cause there ain't one.
- Shake the remote while in the air to do a quick 360. This adds hang time and distance to your jumps by keeping you in the air for a fraction of a second. It ain't much, but every little bit counts, right?
- In multiplayer, the one who gets a 1-up Mushroom gets that extra life for himself. But collecting 100 Coins nets you all one 1-up each, since you all share the same cache of Coins.
- While carrying a player with a Flower Power-up, only they can hit the fire button to launch fireballs/iceballs, but you can spin jump to shoot their projectiles yourself.
- If you're captured by another player somehow (i.e. carried or eaten by their Yoshi), rather than yelling at them to let you go, spin jump to escape.
- The sacrificial Yoshi jump from SMW is still feasible. Shake while mounted in the air to make that extra leap (you monster).
- Frozen midair enemies can be defeated by bumping them from underneath.
- Once frozen enemies float to the surface of water, they stay frozen indefinitely and cannot be broken.
- Standing on Bullet Bill cannons will stop them from firing as long as you're still on it.
- If you're desperate to redo an uncleared level in multiplayer, encase yourselves in a bubble. The level will end as if you all perished, but you'll keep all your lives. You'll all be deprived of current Power-ups, though.
- Ground-pounding a POW Block will activate it, if you prefer not to throw it.