Expert Mode

Expert mode is an option that can be selected during world creation. It greatly increases the difficulty of the game, as well as the quantity and quality of drops. It also offers Expert mode-exclusive items. Expert mode begins the moment the Expert mode world is created, and cannot be altered after that by the player.

General

 * Most enemies have twice as much health, do about twice as much damage, and receive 10% less knockback.
 * Weaker enemies, excluding bosses and their minions, may get an additional multiplier to the above stats in Hardmode and additionally after Plantera has been defeated.
 * Specific enemies (such as all bosses) have additional multipliers to their stats.
 * Enemies and bosses have new AIs with higher difficulty attack patterns.
 * Enemies can spawn near NPCs, although they still will not spawn in front of placed background walls.
 * Enemies drop more loot, including higher chances (usually 50% or 100% extra chance) to drop certain items.
 * Some enemies inflict additional debuffs, or have an increased chance to inflict a debuff that they already inflict.
 * Enemies can pick up coins dropped by enemies or players. Enemies holding dropped coins emit a sparkle effect based on the color of the best coin they are holding.
 * Coins are often lost permanently on death, as enemies who pick up dead players' coins will often despawn once off-screen.
 * Also, picked-up coins will be reset on NPC transformation, therefore the player cannot retrieve coins from enemies like spiders after they have transformed into their alternate form (from horizontal form to wall form, or reverse) or other enemies behaving similarly.
 * Softcore mode players drop 75% of their coins upon death instead of 50%.
 * The general respawn time is increased to 15 seconds, while respawn time during boss fights is increased to 30 seconds.
 * Slime Rain can occur without its usual criteria, spawn rates are 15% higher, and Green/Purple Slimes have a higher spawn chance.
 * Lowering the Celestial Pillars' shields requires killing 150 of their enemies, instead of 100.
 * Killing Pumpkin/Frost Moon enemies progresses the event twice as fast, due to the increased health of their enemies.
 * All NPCs do 1.5× their regular damage.
 * The Traveling Merchant has a 50% chance to sell an additional item.

New enemy attacks

 * Bats have a chance to inflict the Feral Bite debuff.
 * Some Zombies carry a Zombie Arm, causing them to have an extended attack range and higher damage.
 * Spiked Slimes can shoot up to 6 spikes at once in a small area around them.
 * Some Skeletons can throw Bones.
 * Lava Slimes leave behind a block of lava when killed.
 * Jellyfish gain a new shock attack in which they move in a straight line and take no damage. If hit by melee attacks, the player is shocked.
 * Some Black Recluses gain an additional spit attack which renders the player unable to move for a short duration.
 * Granite Elementals can shield themselves from attacks, similar to Granite Golems, but will only do so if they have less than 50% health.

Bosses

 * Bosses in Expert mode have increased health. Their health is boosted even further in multiplayer, with more health added for each player.
 * Each boss has their own boost factor, which is a decimal number greater than 1. For example, Skeletron has a boost factor of 2.0 and Plantera has a boost factor of 1.4.
 * In single player, Expert boss health follows this formula:
 * In multiplayer, Expert bosses multiply their health further based on the number of players:
 * The multiplayer factor is increased incrementally for each player:
 * The base amount of health added per player is 35%. That is,.
 * Each consecutive player adds more health than the last:
 * If there are ten or more players, the multiplayer health boost is modified using this formula:
 * The multiplayer factor cannot exceed 1,000. This limit is never reached in practice because it requires 1,498 players, and Terraria servers cannot have more than 255 players.
 * Boss health is determined at the time the boss is spawned. If a player joins the server after the boss has spawned, the boss's health will not update to account for the additional player.
 * Most bosses gain a new attack or movement pattern which makes them more difficult. For example, Duke Fishron gains a third stage.
 * When defeated, each boss (except for the Lunatic Cultist, Dark Mage, and Ogre) drops an Expert-exclusive Treasure Bag unique to that boss. Each Treasure Bag contains a greater quantity of the boss's usual drops from normal mode, along with unique Expert mode-exclusive items. These items can all be used in non-Expert mode worlds, with the exception of the Demon Heart. Hardmode bosses' Treasure Bags additionally have a 5% chance to contain one random set of developer items. Treasure Bags can be opened in both Expert mode and Normal worlds.

Items

 * Enemies drop 2.5 times as many coins.
 * Pots drop more items when broken, and have higher chances for rare items.
 * Fishing quest rewards give more money, and also have higher chances for better loot.
 * Enemy Banners offer more powerful buffs when placed.
 * Armed Zombie Statues and Bone Skeleton Statues can be found in the world.
 * Hardmode Dungeon enemies have a 50% chance to drop 2 items.
 * Pumpkin Moon and Frost Moon mini-bosses start to have a chance of dropping trophies 5 waves before the normal wave 15.

Player

 * Health regeneration is half as effective (three-quarters with Shiny Stone) without the Well Fed buff.
 * Vampire Knives and Spectre armor healing is slightly less effective.
 * The defense stat is more effective, 50% more effective than in normal mode.
 * When touching the water in a Snow biome, the player is inflicted the Chilled debuff for as long as they stay in the water, and for five seconds after getting out.
 * The debuffs Poisoned, Darkness, Cursed, On Fire!, Bleeding, Confused, Slow, Weak, Silenced, Broken Armor, Cursed Inferno, Frostburn, Chilled, Frozen, Ichor, Venom, and Blackout last twice as long.
 * A sixth accessory slot can be obtained by consuming a Demon Heart, which is an Expert-only item. The slot is permanent, but will only be active if a player is in an Expert mode world.

Expert-exclusive items
Expert mode-exclusive items are found inside Treasure Bags, dropped by bosses, and have the rarity, apart from 0x33's Aviators. While these items can only be obtained via an Expert mode world, they still function in regular worlds, excluding the Demon Heart.

Trivia

 * Expert mode's descriptive text, "", is a quote from the 1984 American action-adventure film .
 * Coincidentally, this same quote was also used as part of the title for a video by Yrimir in his summoner playthrough prior to 1.3.0.1.