Rockfish

This one skips a chunk of the tool grind. Its hammer power sits up where the late pre-Hardmode hammers do, so pulling one out of an underground pond lets you knock down background walls and reshape terrain long before you have mined the ore those hammers ask for.

You have to be fishing below the surface layer, but the biome does not matter, so any cave pond works and a small pool dug near a base will do it. As a weapon it is still a hammer, which means slow and clumsy, so keep it for building and swing something else at enemies.