Jellyfish Diving Gear

The obvious half is that you swim, and your breath bar drains slowly enough that drowning stops being a thing you have to think about. The half people undersell is the light. Submerged, it lights the water around you properly, which turns the Ocean floor and flooded caves from a guessing game into somewhere you can actually see. Out of the water there is a faint glow left over, not enough to explore by but enough to notice.

Every piece of diving equipment writes the same breath value rather than adding to it, so keeping the plain Diving Gear or a helmet in a second slot is a wasted accessory. The Breathing Reed is the exception, since holding one extends the timer further on top.

Arctic Diving Gear is the next step and folds in ice movement. The tell is color: this one glows pink, the arctic version glows blue.