White Mushrooms
If you're lucky enough you may find these harmless mushrooms, they can be found in:

Traverse Town, Red Room. Battle level has to change.
Deep Jungle; Camp and Treehouse
Wonderland; Lotus Forest
Olympus Coliseum, Hades Cup 6th seed. (Make the most of this one)
Agrabah, Treasure Room
Halloween Town; Graveyard
Atlantica; Sunken Ship and Undersea Cave
End of the World; Portal Worlds

They do you no harm, so make the most of it when you find them and try and earn a reward!
Make sure you equip Lucky Strike. Trust me, it helps. ^^;;

Now, in order to win your reward you must hit them with the correct spell.

Here's what to do:

 What The White Mushroom Does  What Spell To Cast
 Light appears over Mushroom's head  Thunder
 Spins  Aero
 Stops moving  Stop
 Shiver  Fire
 Fans instelf  Blizzard
 Floats  Gravity
 Cheer  Donald and Goofy
 Falls over  Cure

And remember to set 3 of these spells as your shortcut and remember that you have to cast the spell quickly before the White Mushroom starts to do something else.

The White Mushroom's usually turn up in three's, so that's three chances to get it right (get one wrong and the Mushroom you were casting on disappears).