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Tekkyū Dosun are large, spiky balls on chains that appear in Super Mario World 2: Yoshi's Island, its remake Yoshi's Island: Super Mario Advance 3, and Yoshi's New Island. They typically appear in castles and forts.
Tekkyū Dosun is wound up by a Boo Guy that sits in the wall. Once it is wound up as far as it will go, the Boo Guy will let go and the heavy ball will drop. If the ball touches Yoshi, Baby Mario will fall off Yoshi's back and the timer will begin. The Boo Guys take some time to wind up these maces, giving Yoshi time to safely pass underneath.
Tekkyū Dosun, as well as the Boo Guys that operate them, are invincible, so Yoshi must time his jumps in order to pass safely.
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