Dryad

The Dryad is an NPC vendor that will spawn once the following criteria have been met:
 * There is an empty House.
 * You have killed at least one Boss.

Once the Dryad has moved into a house, she will tell you the percentage of Corruption vs. Hallow in the game world.

She also sells the following:

Quotes

 * "Be safe; Terraria needs you!"
 * "You must cleanse the world of this corruption."
 * "The sands of time are flowing. And well, you are not aging very gracefully."
 * "What's this about me having more 'bark' than bite?"
 * "So two goblins walk into a bar, and one says to the other, 'Want to get a Goblet of beer?!'"
 * "Why does [Name of Merchant] keep trying to sell me an angel statues? Everyone knows that they don't do anything." (Only if Merchant is present) (There is a typo in the message)
 * "I wish [Name of Arms Dealer] would stop flirting with me. Doesn't he realize I'm 500 years old?" (Only if Arms Dealer is present)
 * "Have you tried using purification powder on the ebonstone of the corruption?" (Only if Eater of Worlds has NOT been defeated)
 * "Have you seen the old man walking around the dungeon? He doesn't look well at all..." (Only if Skeletron has NOT been defeated)

Only during a Blood Moon:
 * "I sell what I want! If you don't like it, too bad."
 * "Dude, is it just me or are there a million zombies out tonight?"
 * "I don't want you to by my stuff. I want you to want to buy my stuff, ok?"
 * "Why do you have to be so confrontational during a time like this?"