Nevermore

The raven is a purchasable upgrade for your forge - buy it (around 3,500 groschen) from the chamber upgrades. The gate is prestige: the option opens up at a high forge prestige level (around 25), so you'll need to have run the smithy for a good while and built its reputation up first. Grind the forge's prestige, save the coin, then buy your clever raven. Not missable.