Shark Tooth Necklace

Penetration subtracts from enemy defense before your damage is worked out, which means its value depends entirely on how small each individual hit is. A rapid fire gun loses a large share of every bullet to enemy armor, so ignoring that armor gives it a big proportional boost. A slow heavy broadsword barely notices. If you are running a Minishark or a Bee Gun into something armored, this accessory is doing more for you than a raw damage increase would.

Any blood moon can drop it, so it is available early, and early is when you should go get it. Once the world flips to hardmode the new spawn table crowds out the blood zombies and dripplers that carry it and the farm gets noticeably slower. A water candle and a battle potion during the blood moon are the standard way to force the spawn count up.

Penetration adds across sources, so this pairs with the Stinger Necklace and the Sharpened buff rather than competing with them. The necklace also feeds directly into its own upgrade later, so nothing you spend getting one goes to waste.