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 a Boss.

Once the Dryad has moved into a house, she will sell the following:

It was believed that the Dryad would only move into wood based rooms, though it is false, but might be implemented [Citation needed].

The Dryad will sometimes talk about how the Merchant keeps trying to sell her an Angel Statue (see quote below). However, if you go and talk to the Merchant he will sometimes say "Angel Statue? No, I'm not a junk dealer".

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."
 * "That merchant keeps trying to sell me an Angel Statue. Everyone knows that they don't do anything."
 * "What's this about me having more 'bark' than bite?"
 * "I wish that gun seller would stop talking to me. Doesn't he realize I'm 500 years old?" (Only if Arms Dealer is present)
 * "So two goblins walk into a bar, and one says to the other, 'Want to get a Gobblet of beer?!'"
 * "Have you seen the old man walking around the dungeon? He doesn't look well at all..." (Only if Skeletron has NOT been defeated)