Item Breakage Avoidance
From Kaizo
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When falling down one tile gap holes with a shell or Goomba in your hand, there may be obstacles on the side that will destroy it. Moving back and fourth as you fall will help preserve the item.
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While holding your shell or Goomba friend with the X/Y button, fall down the gap and press the D pad left or right to avoid the side obstacles. Be careful not hold down the D pad to the sides as you may inadvertently kill Mario by touching whatever is on the sides.