Adventures in the Borderlands
Derandal's Diving Helmet
A strange copper helmet set with panes of crystal, it produces a steady stream of fresh air.
While this helmet is worn, the wearer has a limitless supply of fresh, breathable air. This allows them to avoid suffocation when underwater or to avoid poisonous inhaled gases (such as the stinking cloud or cloudkill spell, or a green dragon’s poisonous breath).
However, due to the limited field of view and muffled sound while wearing the helmet, all Wisdom (Perception) checks are made with disadvantage.
Defeat a challenging creature without aid while both you and your foe are underwater.
Defeat a challenging creature that creates poisonous gas with either a spell or special ability.