The Gnome Skull Masks

From RPGwiki

Technically, these devices are not magical at all, but rather the product of Tinker Gnome technology/insanity. As the name suggests, they look rather like a skull mask. When they are in place, they distort the sound of the wearer's voice. In combination with their appearance, this makes them rather frightening.

The heroes of the Vale used these masks to help them cross the lake of fire at the centre of the continent, where the atmosphere is unbreathable by normal means.