Nymph

The Nymph is a rare enemy that spawns underground. When first encountered, it appears as the Lost Girl, who pretends to be a helpless NPC that needs to be saved. When a player gets close, it transforms and attacks as the Nymph, a dangerous enemy that deals high damage (for a pre-Hardmode enemy). It is arguably the rarest creature in Terraria and is extremely hard to find.

Tips

 * It cannot attack from a distance, nor can it jump very high. Use a ranged weapon from an out-of-reach position.
 * A Harpoon or Flail can be effective, as Nymphs can be stun-locked. Even with its high health, the Harpoon can kill a Nymph in moments with no risk to the wielder, due to its extremely high rate of fire, so long as it is used at short range.

Trivia

 * The Lost Girl appears completely naked. Ironically, it appears often in underground snow biomes, as if it is immune to the cold.
 * In Greek and Latin mythology, a nymph is a lesser female deity with the power to animate nature.
 * Could be inspired by numerous characters in popular culture that bait heroes by appearing harmless and in need of assistance.
 * The left half of the Nymph Banner is of the Lost Girl NPC, while the right half is the Nymph monster.
 * In the Spider Nest there is a background object with an unknown, bound NPC which could be a possible reference to the actual lost girl.