Diving Helmet

Breath is what ends most ocean dives, and this roughly doubles how long you have before the meter starts eating your health. It also slows the damage once you do run out, which matters more than it reads: that is often the difference between drowning killing you and drowning giving you time to swim up.

Every piece of diving equipment gives the same extension and none of them add together, so wearing this next to a later upgrade wastes a slot. The breathing reed is the exception. Holding one multiplies whatever you are already wearing and buys a great deal more time, which is what makes long ocean floor trips practical.

Sharks in the ocean and the deep water pockets at the edges of the map are where these come from. Beyond the raw effect, it is the base for the tinkered version that moves the same ability into an accessory slot and frees your head back up for real armor. That upgrade, not the helmet, is the reason to keep killing sharks.