Certainly Riku wouldn't have known to cut off the tail otherwise. He didn't know that's what he was supposed to do. Fortunately Son Goku had spelled it out quite literally, but he couldn't do anything until he used his Keyblade like so. Well with that attack, though, it seemed like Vegeta was actually forced to shrink in size. The piece of the tail that got cut off was still quivering on the side for the time being. Sora then glared forwards, attacking with a Ki barrage to the downed Vegeta. It almost looked like they didn't even need to taunt him at this rate.