Sunflower

Plant a line of these around your house and the whole area calms down. Fewer things spawn, you move a bit quicker, and the score the game keeps for how evil the surrounding ground is drops for every flower standing. If townsfolk keep refusing a good room and there is corruption or crimson nearby, packing enough flowers in will usually drag that number back under the limit and let them move in.

None of them grow from seed. Every one arrives fully formed, placed by world generation or by your own hand, and the Dryad will sell you as many as you want on any night that is not a Blood Moon. Prying one back up is a pickaxe job, but water also destroys them the moment it touches, so a row that floods disappears with no warning. Placement is fussy: ordinary, hallowed, jungle and ash grass at any altitude will take them, while corrupt grass, crimson grass, mushroom grass, plain dirt, clay pots and planter boxes all refuse.

The two tiles directly beneath each flower can never be converted, even after the world turns hard, and a small pocket around it resists conversion as well. Sometimes that alone is enough to stop infected grass creeping sideways past a gap. A spaced row along the edge of a cleared trench is cheap reinforcement for a quarantine dig. They are fencing rather than a cure, though: you cannot place one on ground that has already gone bad.

The quieter spawns cover critters too. If you are trying to gather worms or fireflies for bait and nothing is appearing, the flowers around your base are why, and they have to come up first. Tombstones work against them one for one, and enough graves piled into the same area shut the buff off completely. That cancellation runs both ways: a few flowers near a spot where you keep dying will stop the place tipping over into a graveyard.

The movement bonus adds on top of a Peace Candle and of Asphalt Blocks, and it also multiplies any speed buffs sitting to its left in your buff bar, so the real boost is larger than the listed one. None of it raises your top running speed once you own Hermes Boots or anything built from them, which is why the speed matters most in the early game and on short hops around a base. They glow faintly after dark, but not enough to count as a room's light source.

Real sunflowers get planted on contaminated ground to draw radiation out of the soil, which lines up neatly with the job they do here. One is also the game's loading icon. A version with a golden center turned up in the 1.3 trailer and never shipped.