From the Super Mario Wiki
Saggy Gummy is an item from Mario Kart Arcade GP and its successor. The item resembles the slime in Slime Time from Mario Party 4. It is a lock on shot item; when a racer locks on an opponent racer ahead, the item homes onto the racer. The item causes initial slow-down, and the main temporary effect is that it stretches the vehicle horizontally and vertically.