Whale

"Poked a whale" - Tyvian saying for "Made a mistake that will definitely get one or more people killed."

A whale is a terrible creature to behold. A grey-skinned behemoth the size of a train, a multitude of flippers propelling it through the water at unimaginable speeds, its many-fanged maws gnashing for the flesh and blood of any beast or man who dares to cross its path. Some citizens of the Empire would claim that whales are gentle and passive, and that they should be protected at all costs. Scores of sailors with dozens of missing limbs lost on whaling expeditions would contend the precise opposite. Indeed, whales are the dominant predator in the open ocean, and, what's more, those who have dared to look beyond the Veil claim to have seen whales swimming through the Void.
Despite the tremendous danger presented by the merest presence of a whale, they are nonetheless hunted in great numbers. Every part of the whale sees use upon capture. Its blubber serves well as both lubricant for machinery and wax for candles. Its bones are sought after for the creation of (mostly illegal) magical artifacts, which can draw on the power of the Void and the Others. Their meat is canned and sold in tins. The most prized substance that can be harvested, though, is the whale's oil. While volatile to the point of being explosive, whale oil is an extremely potent energy source. In cities like Dunwall, whale oil powers the vast majority of technology present, from floodlights and alarms to audiographs and coach cars.