Stretch

Stretches are Boos attached to white platforms that appear in the game Super Mario Bros. 3. They are found exclusively in fortresses and are more of an obstacle than a true enemy. As Mario or Luigi attempt to pass, a Boo will rise from the top and bottom of the platform and attempt to hit him. Stretches are usually found in groups, making them a formidable foe. Stretches can only be defeated with thrown hammers from the Hammer Suit. They're very rare, and only found in two fortresses.

A single Stretch appeared in the Nintendo Comics System short In the Swim! Fun and Sun Fashions, in an advertisement for swimwear, which depicted it lifting weights on a beach. The Stretch, which only had one face, was shaped like a backwards "Z".