Deadly Fog

You create a Fog of necrotic damage, a dense air-born intoxication, like fumes from a coal factory. It's effects vary depending on how large you make the fog's area.                                      Any creature within the fog can only see up to a maximum of 40 feet around them.                                                                                                                                                                                  You can choose to to disperse (end) the spell before it would naturally. Out of combat, this spell takes an hour to prepare and lasts for an

A dense cloud of 5 feet by 5 by 5 would deal 10d8 necrotic damage per turn that it's breathed in for, whereas a 100 by 100 by 10-50f cloud would deal 4d8 per turn it's breathed in for. To engulf an entire village or town in a fog cloud, it's effects are reduced significantly, only making creatures cough and wheeze with mild headaches instead of taking damage