Toxomister

Toxomister, called Puwazone (プワゾーン) in the Japanese Manual, is a badnik from Sonic & Knuckles found in Lava Reef Zone. The badnik is a mechanical tube that produces a toxic cloud of mist that floats up (or down, depending on whether or not the badnik is on the ceiling). If Sonic or Knuckles touches the cloud, the cloud will stick on to him, making him lose rings at the rate of one a second and making his jump height decrease. If the cloud is on Sonic or Knuckles and he has no rings, he instantly loses a life. You can get rid of the cloud by spindashing. To destroy the badnik (which will also destroy the cloud), simply jump on red ball atop the mechanical tube.

Oh, and by the way, the mist can still stick on to you and make you lose rings when you are invincible, have a shield, or are in Super/Hyper form.