In Yoshi's debut, he didn't have many abilities, with the main one being involving his tongue. He could grab most things with his tongue and swallow them, producing coins in Mario World. In Mario World 2: Yoshi's Island, this ability was expanded upon by having Yoshi produce eggs that could be thrown afterwards.
One thing Yoshi has trouble swallowing is Koopa shells, as he holds them in his mouth until he spits them out. However, these added special abilities as he held them in his mouth. The green shell has no special properties, while he would spit out three fireballs with a red shell, gain temporary flight with a blue shell, and produce sand clouds when ground pounding with a yellow shell.
OTHER ABILITIES
Yoshi's jumping capabilities are known to even rival Mario's, as in Mario World, he could kill many enemies in one hit, akin to Mario's spin jump in the same game. He can also do a Ground Pound, similar to Mario in the 3D games, which came into practice starting with Yoshi's Island.
One last move Yoshi is known for is the Flutter Jump, which allows him to hover in the air by holding the jump button. This move easily allowed Yoshi to reach distant platforms, or even rescue himself from death pits. In Mario Galaxy 2, Yoshi is able to infinitely do this maneuver.
TRANSFORMATIONS
In Yoshi's Island, there were transformation bubbles that Yoshi could hit that allowed him to transform into various vehicles. These included a helicopter, mole tank, submarine, car and a train.
In Mario Galaxy 2, there were certain powerups that allowed Yoshi to transform and do special moves. The Dash Pepper gave Yoshi incredible speed for a short period of time. The Bulb Berry turned Yoshi yellow and allowed him to glow, essentially turning him into a light bulb. The Blimp Fruit turned Yoshi light blue and turned him into a blimp, allowing him to fly upwards for a short amount of time.
