Power Flowers are flowers found in game that give you a special power for a short time, for all characters (only the playable ones).
Power Flowers: If you get the ? Blocks to become solid by turning on the hidden ? Switch, and use them, you could get some special powers. Yoshi will get to breathe fire for some time, and can put enemies or items on fire without having to go back and swallowing more fire. Mario will either get wings to go on his cap to fly (and stays longer than the other powers) or he could inflate and fly around. Luigi can turn invisible (mostly transparent) and can go through metal bars or go through some enemies (There is also a room with a mirror that if you enter as Luigi, there will be some Power Flowers around, that you can use to go through the mirror and explore a little) Wario's power is that he can turn invincible, or turn into metal. You can run towards some enemies, and they will be defeated. You won't even lose any health, and can sink in water without swimming, or going in lava, without burning up, but if you stay in lava for a while, you will sink and die.