Nymph

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

The Lost Girl will only transform into a Nymph if one of the following apply:
 * The Lost Girl has been hurt.
 * The distance between the player and the Lost Girl is less than 200 pixels, and she has a direct line of sight to the player.
 * The Lost Girl is moving (falling, knockback).

The Lost Girl is immune to the Confused debuff, but the transformed Nymph is not.

She is one of the few entities that can be detected by the Lifeform Analyzer.