Traps

Nearly every trap you meet was placed by world generation, wired to a trigger, and left for you. A dart trap has a pressure plate somewhere in its line of sight, and that plate can be a long way off, so what kills you is often nowhere near the tile you stepped on.

Two entries are not mechanisms. Spikes and Wooden Spikes simply hurt on contact, and the Land Mine is a hardmode purchase that never generates naturally.

Every trap and every trigger lights up under Dangersense, which makes a Dangersense Potion the best thing you can drink before a deep run. Short of that, wiring is visible while you hold any mechanism, so a spare pressure plate held while you dig is a free early version of the same information. Later a Mechanical Lens or The Grand Design shows wire permanently, in the dark included.

The reusable ones shoot something and reset after a few seconds, so they never run dry. Dart Traps are the common case, spread through the underground and cavern layers and thick in the dungeon.

The temple keeps its own set and they hit harder. Super Dart Traps are upgraded darts, Spiky Ball Traps drop a ball that bounces for a long time before vanishing, Spear Traps stab out a surprising distance on a shorter cycle, and Flame Traps throw fire twenty tiles wide. Flame traps are rare enough that plenty of worlds contain none. Everything there needs a Picksaw to remove.

Geysers are the odd one out. They sit exposed near lava with no wiring and fire when you stand on them, and the flame passes through several blocks, so walling one off may not make the corridor above safe.

The traps that actually kill people are not the ones that shoot.

• Boulder traps. A plate wired to actuated stone with a Boulder on top. Trigger it and the support switches off. In a dark corridor you see neither one.
• Explosive traps. A detonator or buried plate on a large ore vein packed with Explosives. No warning, and the blast will finish a geared hardmode character outright. The vein under one is usually bigger than average, so disarming it pays.
• Sand traps. A block of sand held up by actuators over a plate. It drops and suffocates you, which no amount of defense helps with.
• Lava traps. Same construction with a pool instead. Easy to walk away from, since lava moves slowly.
• Spike pits. A thin layer of cracked dungeon brick over a spike lined shaft. Some are flooded, which is worse going in and a fishing spot later.
• Dead Man's Chests. Gold chests with boulders above, darts to the sides and explosives underneath, all of it firing the moment you open one.

A separate group damages you without being a mechanism. Thorny bushes hurt on contact and break as they do it. Bee Hives hang from jungle ceilings and release a swarm when they break, unless they land in liquid first and die harmlessly. Antlion Eggs sit inert until something hits them. Rolling Cacti barely scratch you standing still, then roll, bounce off walls and hit hard. All of those damage enemies too.

A trap you find is free hardware. Wire and actuators from the Mechanic cost real money, and a generated trap hands you both for the price of a Wire Cutter. Sand traps are the best source, often ten or more actuators each. The Grand Design strips a lava trap from across the screen.

The traps themselves are worth carrying out. Rebuilt into an arena wall they add free damage to every wave of an event, and the pumpkin and frost moons repay a row of dart traps many times over.

Traps hit players roughly twice as hard in expert, on top of the extra damage players already take from them. A warning about exploring rather than building.

Pointed at enemies there is one restriction: everything except the land mine deals half damage to Old One's Army enemies, so a trap wall built for that event does not pay off as it does elsewhere.

Two traps you make yourself. Venom Dart Traps are dart traps rebuilt with spider fangs, hitting harder and applying acid venom instead of poison. Trapped Chests hold nothing and only send a signal when opened, the basis of every player built ambush.

A few types appear only under the No Traps and Zenith seeds, the joke those seeds run on. Gas Traps hide in chests and poison everything nearby when one is next opened, TNT Barrels sit unwired and detonate when struck, and Life Crystal Boulders pose as life crystals until you hit one. That last still drops a real crystal once it stops.