Superheated Blood

Hellstone runs stop needing potions, obsidian gear or a careful approach. You swim straight into the lava and mine from inside it, and the mount thins the lava out visually while you are submerged so you can actually see the ore you are digging toward. Nothing else available that early turns the whole layer into open water.

Out of liquid it crawls, slower than walking with any decent boots. Treat it as something you summon at the edge of a pool and dismiss on the far side rather than a travel mount. It does keep its momentum through the air, so a fast exit from lava launches you a fair distance, and it cancels the fall at the other end.

• Paired with a bottomless bucket you can pour liquid under yourself and swim up through it forever. It takes practice and it leaves a mess, so do not experiment above a base you care about.
• The Wall of Flesh can be fought from inside the lava instead of on a bridge. That saves a long build, but you give up flat ground to dodge on, so run it once in a throwaway world before you commit.

You can still drown. Water and honey move you just as fast but offer no breath, and the Chilled debuff still lands on you, though its slowdown is ignored while you stay mounted.