Capnaps appear to have a full body of feathers with 3 different colors top-to-bottom; yellow, yellow-orange, and orange. They also have two eyes right in front of the yellow feathers. At the top of their bodies, they have two green pieces of grass, at the bottom they have brown feet under their feathers. In the field, like any other enemy they will to chase after Mario and Luigi one they spotted them. However, they also appear to be drowsy as they'll tend to sleep for a few seconds. If Mario and Luigi get closer around this enemy, it will wake up and pursue.
Capnaps can attack in by simply charging straight towards both Mario and Luigi in the foreground or the background. The bros. must both jump to evade the attack. When jumping they can counter on the Capnap. If one of them manages to counter, the Capnap will basically stop and return to its post. Another attack is when, Capnap gets drowsy, falls, and sleepwalks towards a bro. It will start teethering when it towards a bro and then walk straight foward hurting Mario or Luigi. The targeted bro must time the Capnap's teetering and hammer the Capnap before it hurts him.