Dryad

The Dryad is an NPC vendor that will spawn once the following criteria have been met:
 * There is an empty House.
 * Any boss has been defeated (excluding King Slime, Wall of Flesh, and ).

In addition to selling items, the Dryad can report the percentages of Corruption/Crimson vs. Hallow that exist in the current world.

When enemies are nearby, the Dryad will periodically grant the Dryad's Blessing buff to players in the vicinity and displays a leaf barrier effect. The buff grants +8 defense, and gives the player contact damage. Enemies touching the leaf circle of the barrier will take 1 point of damage per second, more if you defeated more bosses (and x1.5 during Expert mode).

World status
The Dryad's reports on Corruption/Crimson/Hallow coverage are accompanied by a status message. She considers Hallow "good", and Corruption or Crimson "bad". The Dryad makes the distinction between Corruption and Crimson if they are present in the same world, and will list their percentages separately, though they both contribute to the overall "bad" total in her final report.

Tips

 * For players creating housing for the Truffle, it would be beneficial to temporarily house the Dryad in or near a Mushroom biome where she will sell Mushroom Seeds.
 * If you can't build a house you can use a Queen Statue to teleport her to a Mushroom biome.
 * Another way to get Mushroom Seeds is to use Boulders or Land Mines to kill the Dryad and make the only valid house in a Mushroom biome.

Names
The Dryad may have any of the following names:

Quotes
After defeating Old One's Army:
 * "Be safe; Terraria needs you!"
 * "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?!'"
 * Tier 1:
 * "When I was in Etheria, I felt so disconnected from [World Name]. Its [sic] good to be back."
 * Tier 2:
 * "The corruption tried to take me over when I went to Etheria, But instead, I used its power against the Old One's Army!"

When Merchant is present: When Arms Dealer is present: When Truffle is present: Before Skeletron is defeated: In a Corrupt world:
 * "Why does [Name of Merchant] keep trying to sell me an angel statues? Everyone knows that they don't do anything."
 * "I wish [Name of Arms Dealer] would stop flirting with me. Doesn't he realize I'm 500 years old?"
 * "I feel like [Name of Truffle] is a bit misunderstood, he really is a fun guy."
 * "Have you seen the old man walking around the dungeon? He doesn't look well at all..."
 * "You must cleanse the world of this corruption."
 * Before defeating the Eater of Worlds
 * "Have you tried using purification powder on the ebonstone of The Corruption?"

In a Crimson world:
 * "You must cleanse the world of this crimson."
 * Before defeating the Brain of Cthulhu:
 * "Have you tried using purification powder on the Crimstone of the Crimson?"

Only during a Blood Moon: When asking for the status Once the world is completely pure: During a party:
 * "I sell what I want! If you don't like it, too bad."
 * "Dude, is it just me or is there like a million zombies out tonight?"
 * "I don't want you to buy 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?"
 * "[Name of world] is [hallow percentage]% hallow and [crimson/corruption percentage]% [crimson/corruption]. [Dryad's comment, see above]."(She will say crimson or corruption depending on which one there is, however if you have corruption and make an artificial crimson biome, she will list both crimson and corrupt percentages, as well as vice versa. She will tell the hallow's percentage in Hardmode.)
 * "[Name of World] is completely pure. You have done an amazing job!"
 * "I thought I would throw a party to celebrate our victories in the past, and those yet to be had."

Trivia

 * A is a nature spirit from Greek mythology, generally depicted as a beautiful young woman. Fittingly, many of the Dryad's possible names take inspiration from either classical literature (e.g., , , ) or female celebrities.
 * This might be the reason that the Arms Dealer appears to flirt with her as shown in one of his quotes, but she states in one of her quotes that she wishes the Arms Dealer would stop pestering her.
 * In the same quote she reveals that she is 500 years old.
 * The Dryad is depicted in a Painting called Dryadisque.
 * Her quote calling the Truffle a "fun guy" plays on the "".
 * One of the Dryad's quotes about the player's safety says "Terraria needs you," instead of "[World Name] needs you." This is an oddity among the other quotes.
 * Calista the Dryad is featured in the Terraria Comic Book from DC Comics.
 * The Dryad also appears in Dungeon Defenders II.
 * The Dryad's quote referencing her time in Etheria and her use of the corruption against the Old One's Army is a reference to her ability in Dungeon Defenders 2 where she can become a corrupted version of herself to do extra damage.
 * One of The Dryad's names (Nissa) comes from the planeswalker Nissa Revane from the trading card game,.

History
Dryade Dryade 드라이어드 树妖