It might seem strange to call the clock a guide, since it's not a person. But so what if it's a clock? The clock is the one force in the story that constantly reminds Prince Prospero and the revelers that time is flying by and they're going to die. They just never listen to it for long. Is the clock a source of good or evil? It's hard to say. It certainly seems scary enough, and it broadcasts a message that no one wants to hear, warning of death's advance. That might align it with the Red Death. Then again, it dies with the last of the revelers – it's a victim of the Red Death just like everyone else. Maybe it was a force of good after all.