Celestial Stone

This is the sun and moon halves welded together, which means you stop paying attention to the clock. Before it you were either swapping accessories at dusk or accepting that half of every day ran at reduced stats. After it the bonus is simply always on.

None of it is dramatic in isolation. What makes the slot worth it is the breadth: damage for whichever class you happen to be playing, a bit of defense, faster mining, and a regeneration tick that adds to a Band of Regeneration instead of overwriting it.

Combine it with a Moon Shell the moment you have both. The shell keeps everything this gives and adds the werewolf and merfolk forms on top, so there is no situation where holding onto the plain stone is correct. Wearing it next to the shell, or next to either of its own ingredients, does nothing at all.