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Koffnix's toxins work their way up from the tip of the tail before being exhaled through the segments closer to its head. Its poison works particularly well on Rock-types, so many underground denizens give it a wide berth.

There is a magnet in its brain that prevents an Koffnix from losing direction while tunneling. Getting up close to a Koffnix will give you a chance to observe, through its thin skin, the toxic gases swirling inside.