Magic Ball

A '''? Ball' is an item in Super Mario Bros. 3 and Super Mario World''. It is required to clear certain levels and activates when Mario or Luigi touch it.

Super Mario Bros. 3
? Balls first appeared in Super Mario Bros. 3 and its remakes. They only appear in fortresses after the player defeats Boom Boom. Then he will release a ball and Mario must touch to destroy the fortress and then win the level. If Boom Boom is touched by Invincible Mario, the ? Ball will appear upside down.

Super Mario World
Only one ? Ball appears in Super Mario World, and that is in the Sunken Ghost Ship (this is most likely to give this level the feel of Super Mario Bros. 3, as it is suggested to be one of the Airships from that game). Touching it beats the level, but it is left out in the open instead of being held by a mini-boss.