Gungnir

A spear is a held stab, not a swing, so the weapon lives entirely on reach and timing. This one reaches further than any other spear, and the burst it makes at the point adds a small pocket of damage past the tip, which forgives being slightly out of position. Against a worm boss you can plant your feet and let segment after segment feed into the same thrust. Against anything that circles you it is much worse, since every thrust commits to one direction and cannot be redirected partway through.

It arrives once your first mechanical boss is dead and holds up while you gather better gear. Melee speed does double duty here, raising both how often you can stab and how far the shaft extends. The glow it leaves behind is a real convenience underground, since it lights the ground ahead of you while you fight.

In Norse myth, Gungnir is Odin's spear, the one that always finds its mark after it leaves his hand. A fitting name for a weapon you cannot actually throw.