Copper Shortsword

Shortswords stab straight ahead with almost no reach, and this is the feeblest one in the game, so the natural instinct is to dump it in a chest and never look back. Two things make that a mistake. It goes into the Zenith recipe much later, and if your world rolled Tin instead of Copper you will not find one lying around anywhere. Shimmer, crates, slime bonus drops and the Chlorophyte Extractinator can all get you a copper bar eventually, but it is far less annoying to hang onto the one you spawned holding.

Clearing a boss with nothing but the starter sword is a standing community challenge, and the demand for it turns up under basically every Terraria speedrun or no-hit run. Re-Logic played along by putting the sword at the head of the Zenith chain, where it represents the start of a character's run, and by adding a True Copper Shortsword on top of that. One other quirk: throwing one at a slime unlocks the Squire Slime.