Remix

You spawn on an ash island in the middle of the Underworld with no hellstone on it, and everything above you is arranged backwards. The layer names stay put while their contents swap. The underground layer behaves as the cavern layer for spawns, fishing and soul drops, and the cavern layer behaves as a surface, with trees, grass, standing water and weather. Both the jungle temple and the dungeon sit out in the open on the real surface. That fake surface counts as ocean about half the time when spawning things, so ocean critters, ocean enemies and the Angler turn up down there.

Every part of the real surface is corruption or crimson, at the spawn rate that implies. The sun never rises, so it stays dark with a starry background where biome art normally sits. Gravity is thin, roughly what a featherfall potion gives you, and fall damage is gone. Floating islands are built from the world evil's blocks, though their chests hold normal loot. Climb high enough and you leave the top of the world, which kills you.

Digging a shaft toward the surface is the obvious plan and the one that kills people. Lava sits in quantity just under the surface along with lava traps, and one wrong tile drains all of it into the tunnel you are standing in. Sand and silt do the same by collapsing when you mine what holds them up. Light everything, check tiles before breaking them, and carry Rope.

Floating islands are worse than the climb. In low gravity, knockback lifts you faster than gravity pulls you back, so with Harpies swarming you can be juggled off the top of the world with nothing to grab. A hook or a Cobalt Shield matters more than damage up there. Thin gravity pays off once: jump accessories and the Shield of Cthulhu let you skim the surface for scouting long before you could survive a fight there.

Lava does vastly more contact damage than usual and the burn lasts several times longer. Enemies, meanwhile, take none of the contact damage and only catch a short burn. That kills the standard lava moat: it will not hurt what you built it against, and it will delete you the first time you slip. The Ash Wood set is the counterweight, since its bonus cuts lava damage far more than usual.

A list of weapons trades places in progression with a partner, keeping its appearance and taking the other's power level and acquisition method. It only applies in this seed: bring one elsewhere and it reverts.

• Falling to the bottom: the Bubble Gun becomes weak dungeon chest filler, the Ice Bow turns into frozen chest loot, and the Magic Dagger is a cheap Skeleton Merchant purchase.
• Climbing: the Wand of Sparking becomes a hardmode mimic drop that autofires and burns, the Chain Knife off clowns doubles its reach, the Snowball Cannon turns into a fast ammo saving gun, and the Flower of Fire comes off red devils as a real hardmode weapon.
• The standouts are the Aqua Scepter, now a Duke Fishron drop, and the Unholy Trident, which falls to shadow chest loot and is still stronger than anything else available at that point.

The Tax Collector replaces the Guide as your starting resident, and happiness is switched off entirely: prices never move, the dialogue option is gone, and pylons sell regardless of where anyone lives, including inside an evil biome.

Placement is rewritten in exchange. The Forest Pylon has to sit below the cavern layer and will not work on the surface no matter how much you purify around it. The Ocean Pylon works almost anywhere outside the center of the world, but nobody sells one up top, so buy it low and carry it. A fast route to the top otherwise means a Teleporter or a Magic Conch.

Biome cleanup is mostly gone. The Steampunker stocks no Clentaminator and no solutions, and the Dryad loses the thrown powders. Import both from another world or do without.

A fully corrupt surface sounds like a Hardmode disaster and mostly is not. The pure part of the world is a rectangle, so containment tunnels run along the axes rather than the diagonal stripes normal worlds force on you. Two stacked horizontal tunnels under the surface, with minecart track to block vines and rope down the sides to stop thorns, seals the top edge. When the Wall of Flesh dies, the Hallow overwrites one of the existing evil strips on the jungle side instead of carving a fresh V, and no new evil is generated, so purity does not fall at all when Hardmode starts. All of that can be dug in advance, since the evil never moves.

The central band of the Underworld you spawn in will not produce hellbats, demons, lava bats or red devils, so a town built there turns spawns into critters almost immediately. Gem critters appear often enough to be real coin income, and once you have Hellstone the local critters make good bait. The lava dwellers need a Lavaproof Bug Net, gated behind an evil biome boss unless you get lucky with a Golden Bug Net from angler quests. Pots down there hold rope and fallen stars.

Events shift too. Slime Rain cannot happen. Solar Eclipses affect only the cavern layer and the Underworld, leaving the surface alone. Bosses normally restricted to night can be summoned whenever you like and will not enrage or despawn in daylight, so Skeletron runs on your schedule. The Empress of Light is the exception in the other direction: fine below the surface, instantly enraged the moment she reaches it, so summoning her up top at night ends the fight before it starts.