Nosk

Behaviour and Tactics
The Nosk is a secret boss found in Deepnest that guards a Pale Ore in the room beside it.

Location
A breakable wall in the room directly left of the Deepnest Hot Spring will reveal a secret section that contains a Grub. Breaking another wall behind the Grub leads to the tunnels that lead into its lair.

When first encountered in Deepnest, Nosk looks exactly like The Knight and will appear in several places that are always out of reach. Once the player reaches the location where it appeared, Nosk will have vanished.

Once reaching its lair, they will reveal their true form through a transformation sequence before roaring and beginning the fight.

Trivia
"'No data available. This creature has been stalking the caverns lately. Travellers are advised to avoid it - it is potentially dangerous.'" Носк
 * In a Kickstarter update there's an entry named "Unknown Species" that could be referring to either Nosk or the Knight, with the following description:
 * Using the Dream Nail on the many victims found throughout the corridors will reveal that Nosk took the shape of their lost loved ones to lure them into his lair.
 * Curiously, some of their victims appear to be Vessels, like the player.
 * It is possible to damage Nosk in its disguised form with the Vengeful Spirit/Shade Soul Spell before the fight begins. This damage carries over to the rest of the fight. However, if Nosk is killed before the actual fight begins, the door to the Pale Ore will not open and the player will be trapped in the room. The player is able to reload their save and fight Nosk again to get the Ore.
 * When it dies, Nosk drops the same mask the player drops upon death.
 * In Nosk's lair, in the background, you can see that one of his former victims is missing a head. This is possibly where Nosk acquired the mask for its disguise.