Iron ball

Big Steelies are large invincible balls that appeared in Super Mario World in the last battle with Bowser. He drops these from his Koopa Clown Car. Mario can jump over them to avoid getting hit. Mario can also spin jump on them without getting hurt.

In the Super Mario World episode "Send in the Clown", Bowser attempts to defeat Mario in one scene by dropping a Big Steely on him, which Mario dodges.

A similar object appears in Super Mario 64. It also appears in the DS remake of the game, Super Mario 64 DS. They appear in Bob-omb Battlefield, Tall Tall Mountain, Tiny-Huge Island, and Battle Fort.