Puff and Blow each have a Methane Gas Gun which fires a cloud of
immobilising gas. If this comes into contact with a bad guy he will be
absorbed into the gas and then float around the screen for a limited
time. Bad guys are harmless in this state. Puff and Blow must suck the
floating gas clouds into their guns and blast them out against a
vertical surface. Bad guys then turn into bonuses which can be
collected. Be warned! - the gas cloud dissolves with time after which
baddies become active again and extremely annoyed.

WWW: http://methane.sourceforge.net/