Pitfall

The Pitfall is an item confirmed to appear in Brawl. It hails from the Animal Crossing series. When set on the ground, the next person to walk over it is sucked down. This also happens when the item is thrown at an enemy. If used on a floating platform, the character will fall through it, but if used on the ground, the character will just be stuck temporarily as if hit by Donkey Kong's Headbutt.

In the Animal Crossing series, it was a fairly common item that, when buried, would cause any character who walked over it to be sucked down into a small pit.

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Confirmation