Guide:Surviving in the Hallow

Overview
After defeating the Wall of Flesh, you may notice a strange, colorful biome with rainbows, unicorns and pixies. This biome is called the Hallow. It is one of two biomes generated after you killed the Wall of Flesh, the other being the Underground Corruption/Crimson. The Hallow is a very deceptively difficult biome, and the three mobs you find on the surface (and the four underground) can be very threatening. To deal with these mobs, it is advisable you have:
 * For Melee: A Night's Edge/Breaker Blade, the Night's Edge is good for damage and knock back, the Breaker Blade is good for reach.
 * For Ranged: A Handgun or Clockwork Assault Rifle may be good to keep most mobs away from you. A Molten Fury or Hellwing Bow may be useful as well.
 * For Magic: A Flamelash is a great weapon to use for damage, and a Space Gun can be used to keep Unicorns and Pixies at bay. Your first aim should be to get a Crystal Serpent (1/200 chance from fishing in the Hallow)
 * For Summoner: You should not enter the Hallow until properly equipped with a Spider Staff. Most Pre-Hardmode summons cause too little damage to be effective against the large numbers of mobs rushing at you in the Hallow.
 * Yoyos are very useful if you are well practiced. An Amarok (1/75 drop from the Snow Biome) can do a lot of damage. A Hel-Fire is similar, and inflicts On Fire!.
 * Roughly 30 defense or more. It helps negate some of the high damage that Pixies, Unicorns, and Gastropods do.
 * Movement accessories, such as Lightning Boots or a Blue Horseshoe Balloon.
 * It is almost required you have at minimum 300 Health. 400 is recommended, as the extra 100 health may be what saves you from the mobs in the Hallow.
 * A Reaver Shark or Molten Pickaxe is a good pickaxe to have around, especially the Reaver Shark, for it is slightly faster.

Surviving
When first interacting with the Hallow, you will notice a sparkling yellow ball. This is a Pixie. It has high damage and health, but is moderately easy to knock around. It is the most common enemy in the Hallow. It shouldn't be a problem unless you have little mobility.

A Unicorn (which does not need to be described as it is pretty much straight forward looking) is a very fast mob that has high health, knock back resistance, and damage. This mob is most likely what will cause you the most trouble. You must be able to dodge well to avoid their charge attack, which can surprise you easily if it spawns off-screen. Most Rangers, Mages, and Summoners should not have much trouble if they are able to avoid its attack, but if you are strictly melee, you should attempt to use a Yoyo to slow them down.

At night, you will find a Gastropod. It has high health, defense, and can shoot lasers. It is the bane of new players in the Hallow, and can kill you quite easily if you aren't properly protected. A high damage weapon is recommended to take them out easily before they cause to much trouble. Most melee users shouldn't find them a problem, but if you use projectiles, you may find them hard to hit. At this point it is recommended you have built up some defense (Warding Accessories, high tier armor, etc.) to negate their damage.

In the Underground Hallow, you will find stronger mobs. It is suggested you don't go here unless you have a significant defense and health. Here you will find the below 4 mobs.

An Illuminant Slime is the slime of the Hallow. It is not hard to deal with, as you've most likely been dealing with slimes from the start of the game.

Illuminant Bats are another difficult mob to deal with. If you don't have Wings or a substantial movement accessory, you should avoid these as much as possible. They are fast, large, and can follow you pretty easily. However, most strategies that work on Cave Bats or Giant Bats work just as well on Illuminant Bats.

Chaos Elementals are the most dangerous when venturing the Underground Hallow. They are able to teleport, and have high health. They operate on Fighter AI, though, and it is easy to jump over them to attack, or keep distance. Keep in mind if you stay within a certain range, they can teleport to you, and without a Cobalt or Obsidian Shield, you might be knocked around quite a bit.

Enchanted Swords are especially difficult in small areas. They move through blocks, and charge towards you. Before charging though, they spin, and you may be able to attack them and deal a lot of damage.

In Expert mode, you may gain a "Shield of Cthulhu" from the Eye of Cthulhu's treasure bag. It is useful against most mobs in the hallow, but requires a lot of practice so you don't throw yourself into danger. The Worm Scarf, if reforged to Warding, can negate a lot of damage, and make the hallow a bit easier if you have a low defense.

Enemies
The hallow has several types of enemies. These include:

(while raining)

At night:

In a Hallowed Desert:

In the Underground Hallow: Enchanted Sword

Resources
The main resources you'll find are Pixie Dust, Crystal Shards, Light Shards, Souls of Light, and Unicorn Horns. Most of these are necessary for game advancement (Pixie Dust and Crystal Shards are 100% necessary, for Greater Healing Potions, something that won't be eclipsed until Post-Lunar Events.) Pixie Dust can also be used for a number of items such as Fairy Wings, the Meteor Staff, and Holy Arrows, a very strong arrow that you will find useful throughout the game. Crystal Shards can be used for a multitude of items, such as Crystal Bullets, and the Chik, incase you are unable to obtain a Amarok or Hel-Fire. Light Shards can be used to create the Dao of Pow and Sky Fracture,two strong early hardmode weapons, and Unicorn Horns are used for the Rainbow Rod. Souls of Light are an essential Pre-Mechs item, used for Boss Summoners, Keys of Light (For summoning Hallowed Mimics), and Angel Wings.