Shell (flashing)

A flashing shell (or flashing Shell ), also described as a flashing kamikaze Koopa shell, flashing Koopa shell, crazy Koopa, or flashing Koopa Troopa shell, is a type of Koopa Shell found only in Super Mario World and its GBA remake, Super Mario World: Super Mario Advance 2. It is created when a yellow Koopa without a Shell climbs into an empty one of any color (including its own, after being ejected from it), thus creating a flashing shell. After its transformation, the shell attempts to hit Mario or Luigi by spinning around and dashing towards him. It becomes impossible to separate the Koopa from it.

Flashing shells first appear in Donut Plains 4. Jumping on a flashing shell causes the Mario Bros. to bounce upwards, but it does not damage it. Flashing shells can be defeated only with a Yoshi, a Spin Jump, or a Super Star. If any Yoshi eats one, it obtains all three shell abilities (causing sand clouds, flying, and breathing fire), as long as the shell stays in the Yoshi's mouth. It is possible to respawn the yellow Koopa without a Shell that climbed into the shell, possibly leading to it dodging its own shell.

After the player beats the Special Zone (or completes all 96 exits in Super Mario Advance 2), all Koopa Troopa and Koopa Paratroopa shells become Mario masks, including flashing shells.