I'm on a roll lately aren't I?
Power-ups, power-ups, power-ups. Mario's seen 'em all. He can shoot fire and ice, throw hammers, fly in like five or six different ways, protect himself from harm or turn indestructible outright. Surely you as Mario fans have had ideas for new power-ups at some point in your young lives. Here's a topic where you can post them.
As usual, here are mine:
Bob-Omb Mario
This is from the file select screen in Super Mario Land 2, where Mario would have to turn into a Bob-Omb to erase a file. I often wondered why they never made that an actual power-up. Were it up to me, I'd have it function similarly to the Blast Mask from Majora's Mask or Detonator Banjo from Banjo-Tooie, minus the health loss. Your main method of attack would be blowing yourself up. This would also be useful for destroying barriers. One another ability I'd throw in is for Mario to be loaded into a cannon and fired, perfect for hitting far away or very high targets.
Jetpack Mario
If there's one thing I liked about Super Mario Sunshine, it's the fact that the game gave you a hover ability in the form of the Hover Nozzle. 3D Platformers tend to benefit greatly from this as it eliminates a lot of the frustration involved in falling from a great height on those vertical levels. Thus, the Jetpack Suit would be next in the hierarchy of flight power-ups. Unlike FLUDD, this would be a regular power-up like the Super Leaf or Cape. It's very useful if you have it, but if you get hit you lose it. In addition, I'd also give this item it's own version of the Rocket Nozzle and Turbo Nozzle, and maybe even full-fledged flight. Said flight would operate like a slower, more precise Wing Cap, with the ability to do barrel rolls and loop-de-loops. Admit it, you know this would make an awesome power-up.
Leaf Mario
Tanookis are known for using leaves and are sometimes depicted as using them as weapons, such as in Pocky & Rocky. I figured Tanooki Mario should have leaf projectiles to differentiate it from the regular Raccoon Suit, but if not than I'd at least have some sort of Leaf Suit. Unlike Fire/Ice Balls the leaves would travel in a straight line but would fizzle out rather than continuing to the edge of the screen. In addition to defeating enemies the leaves would be able to transform blocks into other objects like coins, since they're typically depicted as having magical properties.