Dart Pistol

Crimson Mimic is the source, so this is a mid-Hardmode weapon gated behind hunting mimics in the underground Crimson. Corruption worlds get the Dart Rifle instead of this, and there is no way to have both without visiting a second world.

The rifle hits harder per shot and fires slower. This one does the opposite. Over time they land in almost the same place, so which evil your world rolled decides your weapon rather than which is actually better. The faster trigger does favor darts whose value comes from applying an effect rather than from raw impact, which is most of them.

• Ichor Dart for bosses and anything with real defense. They split into more darts partway to the target, so you still land hits while you are busy dodging, and the debuff they apply stays worth having long after this gun has been retired.
• Crystal Dart in enclosed space or against a clump of enemies. The bounces mean one shot can connect several times in a corridor and mean nothing at all in the open.
• Cursed Dart for grounded packs, and for The Destroyer if you fire from above it. The catch in a Crimson world is sourcing them: that means buying Corrupt Seeds from the Dryad in a graveyard and growing an artificial patch, or hauling materials in from elsewhere.

Darts are their own ammunition pool, which is the quiet advantage. Your other guns keep eating bullets and arrows and nothing competes for the same stack, so you are never switching ammo types mid-fight. The game files it as a dart weapon rather than a gun, which means the Shroomite Helmet bonus applies to it and the Rifle Scope and its upgrades do nothing at all. Unreal is the modifier to want.

It will fire Seed ammunition, at which point it is a very fast, very weak blowgun. Unlike the Blowpipe it does not let you recover the seeds afterward, so this is a curiosity rather than a budget option.