Nymph

The Nymph is a very rare enemy that spawns in the cavern layer. When encountered, it appears as the Lost Girl, who seems to be a helpless NPC in need of rescue. When a player gets close, it transforms and attacks as the Nymph, a dangerous enemy that deals high damage (for a pre-Hardmode enemy).

Achievement
Deceiver of Fools is the achievement you earn for killing a Nymph for the first time.

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, Flail or Yoyo 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.
 * Any high rate of fire weapon will be very effective, as they cannot approach you enough for their attacks to hit.
 * A Hunter Potion, Lifeform Analyzer or both can be useful for finding Nymphs.
 * Using a farm in the Underground Snow is a good way to farm Nymphs. A summoner is recommended.
 * In Expert Mode, the Lost Girl form has twice the health of a normal friendly NPC. This makes it suspicious even on a first time encounter.

Trivia

 * In Greek and Latin mythology, a nymph is a lesser female deity who served the god of nature, Pan.
 * The left half of the Nymph Banner is of the Lost Girl, while the right half is the actual Nymph monster.