Wall of Flesh

The  (commonly abbreviated as WoF) is an aptly named wall made out of flesh that has the height of the entire map. It is the main boss of the Underworld, and defeating it in a world will permanently activate Hard Mode for that world. It is summoned only when the Guide is killed by allowing a Guide Voodoo Doll to fall into lava in the Underworld. The Wall of Flesh moves constantly in the same direction, forcing the player into an on-the-run battle.

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Summoning

 * There are currently several bugs associated with summoning the Wall of Flesh. Please see the Bugs section for more details.

For the Wall of Flesh to be summoned, the Guide Voodoo Doll must fall into lava in the Underworld, and the Guide must die as a result. If the Guide is currently dead when the doll falls into lava, the Wall of Flesh will not spawn because the Guide cannot die if he's already dead in the first place. The Guide must die and the message "[Guide's name] was slain..." must appear at the bottom-left corner of the screen. Killing the Guide by any other means will not spawn the Wall of Flesh. The doll must fall into lava and this must occur in the Underworld. After defeating the wall of flesh, the Pwnhammer is dropped, allowing the player to destroy Demon Altars to "bless" their world with some items and ores including Adamantite ore, Mythril ore and Cobalt ore.

A second Wall of Flesh cannot be summoned if one is currently alive in the world. However, it's possible to consecutively summon the Wall of Flesh on the same world, as long as they are summoned and slain one at a time. (There is a glitch that has caused multiple summons before.)

Warning: Slaying a Voodoo Demon while it's flying over lava and not catching the doll before it falls into the lava can and will spawn the Wall of Flesh. It is usually preferable to spawn the Wall of Flesh by dropping the doll into lava from the player's inventory.

When the Wall of Flesh is summoned, it will always spawn off the edge of the screen and begin travelling towards the world spawn point at the center of the map.
 * If the doll falls into lava closer to the left edge of the map, then the Wall of Flesh will come from the left and travel towards the right.
 * If the doll falls into lava closer to the right edge of the map, then the Wall of Flesh will come from the right and travel towards the left.

Attempting to Escape

 * There are currently several bugs associated with the debuffs inflicted by the Wall of Flesh. Please see the Bugs section for more details.

When summoned, the Wall of Flesh inflicts all players in the Underworld with a debuff called Horrified. Horrified prevents the player from leaving the Underworld until they die or the Wall of Flesh is defeated. Attempting to use the Magic Mirror or leaving the server and coming back while the Horrified debuff is in effect will cause the player to explode upon arrival at their spawn point, and the message "[Player's name] tried to escape." will appear in the bottom-left corner of the screen.

If the player attempts to get behind the Wall of Flesh by any means, it will use a long tongue to pull the player in front of it again, inflicting The Tongue debuff. While The Tongue debuff is in effect, the player cannot move or use items, and will likely take a large amount of damage as a result.

The Tongue may also come into play if the player simply stops moving or if they run too far away from the Wall of Flesh. Note that The Tongue is able to force the player to pass through solid blocks in the process of pulling them along.

Characteristics
The Wall of Flesh has two eyes that shoot lasers, and one mouth in the middle. These three locations are its vital points, and they share a combined 8000 health. Damaging the eyes or mouth is the only way to kill the Wall of Flesh. Note that the mouth has 12 defense while the eyes don't have any defense at all, so the eyes are its greatest weak point.

Small, flying enemies called The Hungry float out in front of the Wall of Flesh. Initially, they are attached to the Wall of Flesh, similar to Man Eaters in the Jungle. When The Hungry take enough damage, they detach from the Wall of Flesh and will chase the player.

As the Wall of Flesh loses more and more health, several changes can be noticed. Its mouth will begin to "burp" out small, red worm enemies called Leeches at an alarming rate. Additionally, the wall itself will travel slightly faster and the lasers fired from the eyes will receive increases in damage, speed and frequency. Should any of The Hungry remain alive in the later stages of the battle, they will gain additional defense and their attack rating will increase as well.

The Wall of Flesh will disappear if it reaches the edge of the map, crushing the player if they are in the way. However, should the player die while fighting the Wall of Flesh, it is possible to return to the Underworld and continue the battle. The Tongue will grab the player from a great distance and throw them in front of the Wall of Flesh. When the Wall of Flesh dies, it leaves behind a square of Demonite Bricks containing all of its drops. The message "Wall of Flesh has been defeated!" will appear to mark its death, and the message "The ancient spirits of light and dark have been released." will appear to denote that Hard Mode has been unlocked.

Hard Mode

 * Main Article: Hard Mode

Hard Mode will be permanently unlocked in a world when the Wall of Flesh has been defeated for the first time. In Hard Mode, the Corruption will begin to spread through Stone Blocks and even Sunflowers. To counter this, a new biome known as The Hallow will be generated the moment the Wall of Flesh dies. The hallow and the corruption can spread through one another and together they will spread throughout most of the world.

In Hard Mode, Demon Altars can be destroyed by the Pwnhammer (always dropped by the Wall of Flesh), causing new ores such as Cobalt, Mythril and Adamantite to appear.

Many new enemies are present in Hard Mode, and most notorious among them are the Clown, who uses bombs to blow up the environment and player buildings, and the Corruptor, whose vile spit attack can spread the corruption. One additional NPC, the Wizard is also available in Hard Mode, as are a wide variety of new items and weapons. Powerful new bosses such as The Destroyer, The Twins and Skeletron Prime await the player as well.

Recommended Equipment
The following lists contain some good ideas on what kind of equipment to use when killing the Wall of Flesh for the first time:

Armor

 * A full set of Molten Armor (gives the highest defense, makes melee attacks more effective)
 * A full set of Necro Armor (makes ranged weapons more effective)
 * A full set of Jungle Armor (makes spells more effective)
 * A full set of Meteor Armor (makes space gun 0 mana cost)

Weapons
An effective ranged weapon or spell:
 * Phoenix Blaster with 400+ Meteor Shots or Silver Bullets
 * Demon Scythe with a sufficient number of Mana Potions
 * Minishark with 2000+ bullets for ammo
 * Star Cannon with 200+ Fallen Stars for ammo
 * Molten Fury with Hellfire Arrows, Jester's Arrows or Unholy Arrows
 * Space Gun in case you run out of ammo.
 * Sandgun with 750+ blocks of sand.

A decent melee weapon to deal with swarms of enemies:
 * Night's Edge
 * Muramasa
 * Fiery Greatsword
 * Dark Lance
 * Sunfury

Accessories

 * Cloud in a Bottle or Cloud in a Balloon (double jumping)
 * Spectre Boots (running and flying if player doesn't have a tinkerer's workshop, then Hermes Boots and Rocket Boots )
 * Obsidian Shield (immunity to fire blocks and knockback)
 * Mana Flower (uses mana potions automatically)

Many other accessories including but not limited to the Shackle, Band of Regeneration and Band of Starpower are potentially useful. It is highly recommended to Reforge all accessories as necessary so that they will give defense boosts or attack boosts.

Misc Equipment

 * Grappling Hook or Ivy Whip
 * Grenades or Dynamite (useful on a bridge)

Potions

 * Ironskin Potions (for extra defense)
 * Obsidian Skin Potions or Water Walking Potions (for dealing with lava)
 * Healing Potions (at least 5)
 * Mana Potions (for magic-users only)
 * Thorns Potions (for reflecting damage done by the wall)
 * Gravitation Potions (for flying over/around lava or obstacles)

Any other buff potion is potentially useful.

Tips

 * Always maintain some distance between yourself and the Wall of Flesh so that you don't get The Tongue debuff and so that you don't get hit by its extremely painful melee attack.
 * Make it a high priority to eliminate all of The Hungry, as they will get much stronger as the Wall of Flesh loses more health.
 * The eyes of the Wall of Flesh have 0 defense, while the mouth has 12 defense, so aiming for the eyes will do more damage.
 * A high defense rating (40+) can render lasers and Leeches virtually harmless.
 * Many of the weapons listed above damage multiple targets simultaneously, which is very helpful against The Hungry.
 * Ranged weapons are always advised against the Wall of Flesh, as melee weapons are typically both riskier to use and less effective.
 * Lava and obstacles in the Underworld are one of the greatest threats when fighting the Wall of Flesh, so make sure that you have a way to deal with them.
 * Sometimes it can be difficult to see in the Underworld, so you might want to have a source of light.

Strategies
The following is a list of strategies that can be employed against the Wall of Flesh. This section is concerned mostly with tactics rather than specific equipment choices. For equipment ideas, refer to the Recommended Equipment section above.

Bugs

 * The Horrified debuff might remain on the player after being killed by the Wall of Flesh.
 * There is a bug when you fight Wall of Flesh on a multiplayer server that you start off the fight with The Tongue Debuff.
 * If two or more Wall of flesh spawns, they sometimes spawn invincible and cannot be killed, (this can happen if there are two Guides on the same map)
 * The Wall of Flesh may not drop a Pwnhammer upon death, though this is an extremely rare occurrence.
 * It has been reported that sometimes the Wall of Flesh may not be summoned when a Voodoo Demon is killed above lava (even though the doll falls in the lava and the Guide dies).
 * If the doll falls into lava very far away from the player (completely offscreen), the Wall of Flesh might spawn without eyes, a mouth or The Hungry, and is completely invincible.
 * Sometimes the Wall of Flesh cannot be summoned a second time on the same world.
 * Sometimes after beating, and then teleport back home then next time you start, the world might be gone.
 * Sometimes after you defeat WoF, some Leeches might follow you back to your house if you teleport.
 * If there are multiple guides alive when you drop a Doll in the lava, it will cause the same amount of WoF to spawn and if there are too many of them, it can cause sever lag on a multiplayer server when it becomes impossible to do anything.

Bug Fixes

 * One way to fix the bug when the horrified debuff stays applied after the battle is to enter/create (then enter) a different world, let any monster besides the WoF itself kill you, exit the game, and come back to your main server where you had the Horrified debuff glitch. The debuff will be gone after dying by a monster in another world.
 * Fighting another boss such as Eye of Cthulhu, Eater of Worlds (on the same world) should allow him to be spawned again
 * If the Horrified debuff remains and the Wall of Flesh cannot be summoned, close Terraria and restart it. The debuff should not appear upon returning to The Underworld.
 * If none of the above works and its impossible to summon WoF in any other world then you must make a new character. This can happen if you drop the doll into a hellevator.
 * To rapidly fix the huge lag problem you can always restart the server, causing all of them to despawn.

Trivia

 * Possibly a reference to the Demon Wall boss in Final Fantasy IV, Final Fantasy VII or Final Fantasy XII.
 * If fought and defeated for a second time near a Underground Corruption or Underground Hallow he has a chance to drop a Soul of Night/Light along with his other items, which can end up being pretty funny seeing it there.

Walkthroughs
Wall of Flesh Solo Guide - by Mathmagician