Potion of Return

It sends you home the way a Recall Potion does, and it leaves the door open behind you. A portal opens at spawn that drops you back exactly where you drank it, once. That turns going home into a round trip instead of the end of your expedition, which is the difference between clearing your inventory mid dig and giving up on the tunnel.

• Drinking a second one deletes the first. Only one exists in the world at a time.
• Leaving the world ends it. It will not be waiting for you tomorrow.
• Both ends show on the map, but you cannot travel from the map the way a pylon lets you. You still have to walk to spawn.
• In multiplayer you can only step through your own. Everyone else's look faded and do nothing.

Mid fight it is a nurse button. Drink, heal, walk back through, and you are in the arena again before most bosses have finished repositioning. That works on anything not tied to a biome, Moon Lord included. It also doubles as an escape hatch when a cave goes wrong: leave, wait a few seconds, and the pack that had you cornered will usually have despawned by the time you come back.