A Moth Cloud comes about when Another One is disconnected from its Void source, usually by ripping it out of the ground. Once disconnected, Another One will take the vague shape of a person and at the same time, draw the attention of all insects in the area, mostly moths. They are apparently attracted to the darkness of the Void and will swarm the "Corpse" of Another One, creating a “cloud."
Once Another One becomes a Corpse, it is completely harmless and will not attack or defend itself; it is only concerned with returning to a dark place. It will often fail in doing this as it doesn't seem to be completely aware of its surroundings and will eventually find its way into the light and melt away.