From the Super Mario Wiki
Potted Ghosts are creatures found in Yoshi's Island DS. They are smaller versions of Roger the Potted Ghost, except their vases look as if they are baskets or clay pots. They rise out of their pots at regular intervals, attempting to catch Yoshi off guard. Yoshi can tip their pots upside-down by shooting them with eggs. Then, the Yoshi can jump on their pots, and when the ghost "rises" downward, it will lift the Yoshi upward, allowing him to reach high ledges. When upside down, the Potted Ghost can move slowly.