Lava Charm

The protection only counts if it is already on when you touch lava. Falling in and then opening your inventory does nothing. Contact starts a timer above your head that counts down like the breath meter, and it refills far more slowly than breath does once you climb out, so repeated dips will drain you dry even though each one felt survivable.

Mining Hellstone stops being a ritual. You can stand in a pool and work instead of pumping it out first, and being knocked into lava mid fight becomes an inconvenience rather than a death. That alone is most of the reason to want one before the Underworld leg of a run.

Each upgrade in the chain adds its own window instead of replacing the last one, and a Demonic Hellcart quietly adds another on top even though it is not part of the family. Filling accessory slots with them is how people get long enough immunity to treat lava as ordinary terrain. Most players never need more than two, but the option exists if you are building an Underworld base.

Only chests in the deep part of the Caverns where lava pools form naturally carry it, so sweeping the upper Caverns is wasted effort. Spelunker Potions plus bombs along an abandoned mine track cover ground quickly. If searching sounds tedious, a Magma Stone off a Hellbat thrown into Shimmer converts straight into one.