All NPC's

Starting

How to get all the NPC's in Terraria. First of all a NPC needs a house to life with his own room or space. This is easy to do. You only have to build with blocks a house and put some wall on the background, and put some lightning in it. Final thing you have to do is to make at the Crafting table one chair and one table and put those in your house. And voila, it's now suitable for NPC's to live in.

so the requirements are:
Enough space (insert tiles)
one chair and one table
background walls
and a door.

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Guide

The Guide will be there at the start if you create a new world.

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Merchant


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Stylist

You can find the Stylist in underground spider nest'. The Stylisy is a regular spawn like an enemy is. So if she isn't at the spider nest. You can kill all the enemies in that area, walk away and come back. Eventually she will spawn.
Make sure you will talk to her otherwise she won't move in your house.

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Angler

The Angler spawns at the beach at the most right of your map or left. He can also float on water or lay behind a tree.
Also make sure to talk to him.


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Truffles

You can't find Truffles and he will only move in on SURFACE mushroom biomes.
A surface mushroom biome won't spawn by world creation, you need to make one by your own. To do this you need to get some Mushroom grass seeds, you can obtain these at underground mushroom biomes from cutting trees and cutting grass.
Place the seeds on a 2 layer mud blocks at the surface. This will spread just like Corruption and Hallow. If it's big enough you can build a house on it and Truffles  will move in.

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Nurse

The Nurse will move in when you consumed atleast one heart crystal.
Heart crystals are found underground.