From the Super Mario Wiki
Bungee Piranhas, or Bungee Piranha Plants, are purple Piranha Plants that use their stem as a bungee cord. They only appear in Yoshi's Island DS. Bungee Piranha Plants are very similar to Elasto-Piranhas. They hang on ceilings, waiting for prey (which is usually a Yoshi) to come along. They then bungee down, attempting to grab their prey. A bigger and boss version called the Big Bungee Piranha appears in World 2's Castle, Big Bungee Piranha's Lair.