Know this people, Loop is among the most ANNOYING Clow Cards. It's main power is to create a continuous loop in space, which will make you repeat thing over and over and over and over and over and over and over and over and . . .you get the picture. It's physical form is basically a loop!
In Episode 21, the gang at Reidenton Elementary ran a marathon, but because of Loop, it wouldn't stop. Sakura, Li, and Madison discovered that Loop was at work. As soon in the picture above, Sakura summoned the Sword Card, and combined with Li's sword they sliced through the point where the loop began, causing it's form to appear so Sakura could seal it. When summoned, it will create a continous loop.
