Fog Machine Mario is one of Mario's Power-up forms that can be obtained if Mario grabs a Fog Machine Suit. When Mario obecomes Fog Machine Mario, he will be wearing a "black box", which symbolizes the the fog machine.
Fog Machine Mario is able to create fog like that of a Foo or Katrina. The fog hides Mario with only his outline hinting at his presece. The fog does not hide enemies, as they appear to "cover" the fog. The fog leaves them wondering where did Mario go, so they just stand still and do not attack.
This is Fog Machine Mario's chance to kill the enemy, as the enemy cannot see him, but still hurts him if Mario and the enemy make contact. The fog does not work on Spike Balls, Rocket Engines, Spike Pistons, obsatcles that are not living, or moving platforms.