OK, here is the official #creatober entry for October 12th!
Plate Armor of Water Breathing
This full plate armor looks typical of its type, except for the helm. The visor of the helm appears to have been replaces with a thick piece of glass that is permanently shut. The wearer can see through this glass easily enough, but it cannot be opened and is completely air tight.
If the wearer of this armor is completely submerged under water, they will find that they are able to breathe completely normally. It is somewhat inaccurate to say they can breathe water, for no water is able to penetrate the armor and the wearer remains completely dry.
Unlike other water breathing magics, this effect is unfortunately of limited duration. The wearer will be able to breathe normally for 1d6 hours, after which they will notice the air becomes quite stale, and the smell of their own sweat fills their nostrils. One more hour later the air is completely unbreathable, and the wearer will begin to be affected by drowning rules just as if they had submerged themselves in normal, non-magical full plate armor.