Iron ball

Big Steelies are large invincible balls that Bowser drops from his Koopa Clown Car in Super Mario World. Mario can Spin Jump to avoid getting crushed by them.

Appearances in Other Media
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.