This glitch works for every character except Lloyd, Genis, and Presea. Get into a battle with the desired character. Perform a basic attack combo and link it to a spell. Quickly cancel it (Guard) and continue the basic attack combo. Repeat. This takes lots of practice. You may want to set Guard to L and hold it down while doing this. Some basic attacks are easier to pull this off with than others, try experimenting.
Submitted by: Matt