The easiest way, by far, is playing a "Capture the Chao" match with a second controller on the Creepy Castle arena. In the central bridge you'll see a Super Object consisting in 6x Ice Shots. Shoot the second player with them and keep waiting for it to respawn so you can shoot again and again until you get the achievement.
Also, if you make 10 of your hits backwards, you'll unlock the achievement for 10 Hits Backwards in a Single Race