Terraspark Boots

This ends the early game shuffle of swapping mobility items in and out. Sprint speed, ice traction, water walking, no fall damage onto a liquid surface and a lava timer all collapse into one slot, and none of it is gated behind a boss. Most of the parts turn up in crates, so a fishing habit gets you most of the way there without a dedicated hunt.

Once wings go on, the boots stop giving you their own hover and hand that time over to the wings instead. Nothing is lost, but it does mean the flight duration quoted for any pair of wings runs a little long whenever these are equipped.

The immunity window stacks with every other lava accessory you own, and a Demonic Hellcart adds to the pile even though it is not part of the upgrade chain. Stack a few and Underworld building stops being a timed run. When the window does expire you still take reduced lava damage and shrug off the burn faster, so it fails gracefully instead of dropping you straight into a death.

For fights they are only average. Amphibian Boots give vertical movement these cannot match, and in an arena that is worth more than walking on water. Keep both and swap by situation rather than treating this as a permanent slot.