Shroomite Bar

The armor is the obvious sink and the right one for anyone who shoots. The set pays you for holding still and the helmet you pick locks the bonus to one ammo type, so decide whether you are an arrow or a bullet player before you start hammering. Finish the set before anything else on this list.

After that, the Hoverboard is the single biggest comfort item in the tier and the Shroomite Digging Claw turns tunneling into something you do at a jog. The Drill Containment Unit is the expensive one and it wants a pile of everything else on top, so treat it as a project rather than a next step.

They come out of the Autohammer and nowhere else, which means the Truffle has to be living in a surface mushroom house and Plantera has to be dead. Build that house early, well before you are ready for the fight, so the bars start flowing the moment she does.