Undyne (ˈʌnˌdaɪn | ᴜɴᴅɪᴇɴ[1]), known as StrongFish91 on the UnderNet, is a fish-like monster that leads the Royal Guard. Clad in her full suit of armor, she pursues the protagonist through the entirety of Waterfall and is frequently evaded or inadvertently thwarted by the Monster Kid.

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