The raven-monster, especially in urban fantasy or hidden-world thrillers, often exists on the axis between a harbinger and an active agent. It's rarely just a scary bird. That intelligence, the ability to speak or mimic, makes it a perfect conduit for ancient knowledge or curses. In a plot, it can be the one creature that knows the secret the human protagonist needs, but it demands a price or speaks in riddles. I love when they're used as familiars to a more powerful, shadowy antagonist—it creates this constant feeling of being watched, that anything you say to a trusted ally might be overheard and repeated back in a twisted caw. It turns the natural world into a surveillance network for the supernatural.
That said, I'm a bit tired of the 'wise old raven guide' trope. Give me a raven-monster that's genuinely malicious, not just a stern teacher. A creature that delights in chaos, picking at the seams of reality because it finds human suffering amusing. That shifts the thriller from a puzzle to a hunt, where the monster is actively engineering the protagonist's breakdown.