Shell (flashing)

A Rainbow Shell is a rare kind of shell found only in Super Mario World. If a Beach Koopa climbs into a Yellow Shell, even if it's not its own shell, it will become invincible, with its shell flashing rainbow colours (turning it into a Rainbow Shell). After its transformation, the Yellow Koopa will attempt to hit Mario or Luigi by spinning around in its shell and dashing towards them. The Mario Bros. can only defeat Yellow Koopas wearing a Rainbow Shell with a Spin Jump or Star. If Yoshi were to eat a Rainbow Shell, he would temporarily get all three shell abilities: make small earthquakes, fly, and spit out fire.