Thorn

Thorns, or Crystals, are spiky obstacles found in Super Mario World 2: Yoshi's Island, Yoshi's Island: Super Mario Advance 3 and its sequels, Yoshi's Island DS and Yoshi's New Island. They are found mostly in castles. Contact with them will immediately defeat a Yoshi. A Yoshi Egg destroys a single thorn, but since thorns are found usually in groups and Yoshi can carry only six Yoshi Eggs at a time, most thorn groups are impossible to destroy. However, in Yoshi's Island DS, Baby Donkey Kong's explosive eggs can easily destroy a group of them in one shot. Sometimes after they are destroyed, the thorns reveal Winged Clouds, and in The Potted Ghost's Castle, one specific thorn reveals even a door.