Weakstone 1

He raised the stone before him, and its rays arched down the steps. The light from this gem did not pass through the air in straight lines; rather it bent in arching curves tinged with a greenish glow.

The light struck the lead su-chi in midstride, as it was climbing a step. The artifact, vigorous and healthy a moment before, now sagged noticeably, as if the vitality had been suddenly leeched from it. It bent forward on the step. The creature behind it was taken by surprise and slipped backward, taking two more with it as it fell. The three collapsed in a pile on the landing, and only two of the figures rose again.

"Didn't stop them," gasped Urza. "Told you."

"Slowed them down," snapped Mishra.

***

The Brother's War, Chapter 4