You’ll encounter various NPCs during your travels through the different Biomes in Terraria, and some of them will want to move to your town. You’ll need to ensure these NPCs have an empty house to move into, how many and which types of NPCs live beside them and what Biome they live in to achieve optimal happiness. The Zoologist, for example, prefers living in the Forest Biome, and you’ll be able to purchase the Leather Whip from them if they’re happy enough. Another upshot of having happy NPCs is that you’ll be able to place Pylons in the Biomes that will allow you to fast travel.
Terraria - How to unlock NPCs and make them happy
Your Bestiary will give you details of who likes what and why, which makes placing NPCs a little easier. There are at least 25 NPCs to find and each has their preferred Biome to live in, neighbours and requirements for unlocking. Each NPC will offer you something unique like recipes, supplies and some can even heal you and remove buffs. If you have at least two happy NPCs in a Biome, you can purchase a Pylon that will allow you to teleport around the world.
Terraria - How to unlock Pylons
You’ll need to make sure that you place each NPC near another that they like in the correct Biome where possible. Once they are happy enough, you can buy Pylons for fast travel. Only specific NPCs sell Pylons and you’ll need to use specific pairs to unlock them:
Zoologist and Guide Arms Dealer and Nurse Mechanic and Goblin Tinkerer Stylist and Angler Clothier and Demolitionist Painter and Dryad Party Girl and Wizard
Once you’ve got a Pylon, place it and you can fast travel between Biomes as long as there are at least two Pylons placed. You can check out this handy guide from HappyDays for more info on Happiness.
Now that you’ve done that, you can check out our guides on where to find every Whip and how to summon and defeat the Empress of Light.