Flower - Makes Luigi invincible to most things. He can go through screens and other objects. Note: Luigi can run on water for a short time. Also, if you jump and hold it, he kicks his feet fast and falls slower. If you try to do a triple jump with Luigi it can be more difficult -- if you hold it for about one second, he kicks and you will not be able to finish the triple jump.
Feather - Jump three times to make Mario fly. Flower - Make mario inflate and float slowly; handles easier than the feather. Note: Mario is just the basic character with no special abilities.
Flower - Metal Wario; he is invincible and can stay underwater. Note: Wario is the slowest character. He also lacks jumping skills, but he is the best at Ground Pounds. He can break black bricks.
Flower - Makes Yoshi's mouth full of flame and can breath fire. If you ever see fire, such as in the basement, you can eat it and can spit fire once. Note: Jump and hold it for about a second. Yoshi will with kick his feet (faster than Luigi) and hover for about two seconds.