Well, you know how Toads always give out items at Toad Houses... well, if Yoshi has Baby Toad on his back, holding Down on the + Pad while pressing the Y button in front of those red tulips... see the picture...
Baby Toad shoots spores at those red tulips... and they become Fire Flowers... like those Fire Flowers that were found on Dinosaur Land...
They turn Yoshi into Fire Yoshi and he throws flaming eggs that melt ice... now, if those tulips were blue... they become Ice Flowers when Baby Toad shoots spores on them... they turn Yoshi into Ice Yoshi and he throws eggs that freeze enemies, including the Nep-Enuts, turning them into temporary platforms.
Remember this pot of flowers?
If Baby Toad shoots spores on them, they grow into a beanstalk flower like this...
And Yoshi can push potted beanstalks around.
Remember this plant that shoots out eggs?
If Baby Toad shoots spores on them, the Egg-Plant starts shooting out giant eggs!
No Fat Guys required!
See that mushroom?
If Baby Toad shoots spores on red mushrooms, they turn into Super Mushrooms... when Yoshi grows bigger, he can actually eat Piranha Plants, Boos, Tap-Taps, Bandits, and other normally inedible enemies. Yoshi also lays giant eggs.
If Baby Toad shoots spores on green mushrooms, they turn into 1-Up Mushrooms.
If Baby Toad shoots spores on mushrooms with different colors, they grow into mushroom platforms like these mushrooms...