Whether ghosts or Dementors, whenever they appeared, the temperature around them dropped rapidly. This was completely opposite to living people, whose presence raised the surrounding temperature.
If understood through the Eastern theory of yin and yang, cold was yin and heat was yang. Yet souls did not always represent yin.
Compared to life, the body was yin, while life was yang.
A dead person still had a body; a corpse was not the same as life. An Inferius summoned by dark magic could move, but that did not mean it possessed life either.
After being struck by the Avada Kedavra curse, a person bore no wounds on their body—Harry Potter excepted—but the result was death: the soul was separated from the body. This was the same result as being killed by the Basilisk's gaze. After her death, Moaning Myrtle had once wanted to haunt Olive Hornby, who had mocked her. But after Olive Hornby reported her to the Ministry of Magic, the Ministry prohibited her revenge. She was restricted to Hogwarts and forbidden from harassing Olive Hornby again.
Myrtle's "superpower" was making the second-floor bathroom soaking wet, somewhat like Kull's ability to whip up hurricanes and create cold storms.
At most, Myrtle could flood the second floor. It was irritating, but it could not cause any real harm. If she were a little stronger, her crying could turn into torrential rain and create a great flood that drowned the world. Then, to make her stop crying, the living would have to find ways to entertain her, perhaps sending two little boys to play with her. Myrtle would become the "Rain Goddess."
Ancient wizards sometimes also served as priests. Once they understood what a "god" wanted, they offered it what it desired—wine, livestock, people, and all manner of strange preferences. Having