Blue Jellyfish Jar

Killing the jellyfish that drift around in water gives you nothing to bottle. The one you need is a bait item that comes up on a fishing line, so the jar is a byproduct of a fishing session rather than of combat. Bottling one is not permanent either: drop a finished jar into shimmer and it comes apart into the jellyfish and the bottle again.

The glow is weak, but it is enough to satisfy the light requirement for NPC housing, so a jar on a shelf can be the only fixture in a room that still counts as valid. It sits on blocks and on platforms, and it keeps glowing underwater, which is where it earns its place. Most lighting either refuses to go in an ocean build or looks wrong there. There is no wire input, so once placed it is on for good.