Ambrosia

One use per character, permanent, and there is no way to get a second. Any fruit thrown into Shimmer becomes one, so do not burn anything rare on it. Apples or Bananas knocked out of the nearest tree work exactly as well as anything you had to hunt for.

The payoff is mining and block placement, not combat, which means it does nothing for a boss fight and quite a lot for the hours around one. On a fresh character you will barely notice. On a character about to dig a hellevator, wall off an arena, or lay out artificial biomes for NPC pylons, the placement speed is the half you actually feel. Take it the first time you reach Shimmer and stop thinking about it.

In Greek myth ambrosia is what the gods ate, and eating it is what kept them from dying.