Leather Whip

This is where whips begin, and the reason to carry one has nothing to do with its own damage. Cracking an enemy tags it, and your minions then hit that target harder and go after it in preference to anything else. A summoner without a whip is doing a fraction of the damage they could be, so the moment the Zoologist moves in this becomes the cheapest upgrade the class can buy.

The swing is slow and the reach is short, so you end up standing closer than you want to be. Treat it as a way to point minions at what needs to die, not as your weapon. Replace it as soon as anything better appears: Snapthorn and the Spinal Tap both outclass it well before Hardmode.

In practice it is always on the shelf. The Bestiary progress needed to unlock the listing is lower than the progress needed to make the Zoologist move in at all, so if she is standing in your town she is selling it.