Molten Skull Rose

A short timer of lava contact plus immunity to burning. That is enough to swim a lava lake, grab what is on the far side and get out, rather than dying on entry. It does not make lava harmless, it makes it a resource you can spend.

Every lava charm derivative you wear adds its own window on top, and the demonic minecart counts even though it is not part of that upgrade line. Anyone doing serious underworld building loads several slots with them and gets a genuinely long dip out of it. For normal play, one is plenty and the rest of your slots are better spent elsewhere.

Both halves of the recipe already contain an Obsidian Skull, and combining them throws the second one away. If you are planning ahead, build toward this directly instead of finishing both parents first, or you will burn an extra skull for nothing.