Undyne debuts in armor varying in light and dark shades of gray, but without armor, is a piscine, anthropomorphic monster.  She has blue scales and a long red ponytail.  She has red and blue fins on the sides of her head, and a pair of sharp, yellow, protruding teeth.  She wears red eyeshadow and has an eyepatch on her left eye.  She also wears a black tank top and jeans.  Her eyes have black vertical pupils and a yellow sclera.  Undyne has no nose.  Undyne is passionate about everything that she does.  She acts quickly on her ideas and is steadfast in her beliefs.  She loves to help others and mentors Shyren and Papyrus in various skills.  Undyne dislikes puzzles, loves japes, and enjoys anime, an affinity she shares with her romantic interest, Alphys.