Don't Dig Up

Don't Dig Up, also known as the "Remix Seed" is a secret world seed introduced in the 1.4.4 update.

The following seeds can be used to generate a "Don't Dig Up" world (case-insensitive):

Changes

 * The player now spawns in The Underworld instead of the surface.
 * The world generates a trapezium-shaped but mostly flat Ash Block "island" in the central part of the Underworld where the player's spawn point is. It consists of Ash Grass and Ash Trees to help start housing in the Underworld.
 * There are 3 underground layers (from top to bottom of the map): The first layer which appears to be the Cavern layer. The second layer which appears to look like the Surface biome by replacing most of the Stone Blocks with Dirt, Grass, and Clay blocks, forest trees and sunflowers generate on the grass. The third layer which is a Glowing Mushroom biome.
 * The surface, the sky islands, and an outer 2 sixths of the world will be infected by the chosen world evil.
 * Touching the top of the map will instantly kill you.
 * Fallen Stars that fall from the sky will not drop the item and instead damage the player if the player hits it.
 * The Dungeon is painted with seemingly random Deep Paint, the walls inside are always painted black.
 * Like the Dungeon, the temple is painted with random Deep Paint and the walls inside are always painted black.
 * The temple spawns on top of the Jungle, where the surface is so you would have to mine all the way to the surface to reach it.
 * The world will always be night. Attempting to change the time to daytime on the Journey Mode Power Menu will not change it to daytime.

NPC Changes

 * The Tax Collector replaces the Guide as the starting NPC.
 * Mimics now spawn in Pre-Hardmode.
 * Lava Slimes no longer generate lava upon death regardless of difficulty.
 * The Steampunker no longer sells the Clentaminator.

Items Changes

 * The Unholy Trident is now found in Shadow Chests and has reduced base damage.
 * It is swapped with the Flower of Fire which instead drops from Red Devils and has increased base damage.
 * The Katana is no longer sold by the Traveling Merchant, but instead drops from Bone Lee in the Dungeon and has increased base damage.
 * The Keybrand is sold in place of the Katana, and has reduced base damage.
 * The Ice Bow can be found in Ice Chests and has reduced base damage.
 * The Snowball Cannon has increased base damage and attack speed.
 * The KO Cannon has lower base damage and attack speed.
 * Underground Hallow will take the place of the world evil at one of the two world edges, when Hardmode begins.
 * The Bubble Gun is now found in the locked chests in the Dungeon and has its damage decreased.
 * It is swapped with the Aqua Scepter, which instead drops from Duke Fishron.
 * Mimics drop Gold Chest loot during Pre-Hardmode.
 * Mimics revert to normal loot once Hardmode begins.
 * The Wand of Sparking is dropped from Hardmode Mimics and has a damage and overall stat increase.
 * The Wand of Frosting has also received a similar stat increase.
 * The Magic Dagger can be found pre-Hardmode with reduced damage.
 * Pots have a chance to drop Fallen Stars.
 * Slimes have a chance to contain Fallen Stars as their bonus drop.

While generating

 * The Terraria logo rotates and flips upside down.
 * The background turns into the starry sky background of Space.
 * The Corruption music will be played, regardless of world evil.

World icons
The world icon of a Don't dig up world is an Ash Tree.