Because of its unique birth, compared to most of the neutral elemental creatures, they are the epitome of evil. They take pleasure in causing pain and destruction, especially in setting ablaze places inhabited by creatures, which is also a way for them to reproduce.
When a large number of creatures, especially intelligent ones, are burned to death, varying amounts of new Fire Residue are born, among which the Fae Race are their favorites. The birth rate of Fire Residue is the highest among them.
When there is a volcanic eruption or a large-scale wildfire on the Material Plane, a large number of Fire Residue are often spawned. Once massed together, they fuel the blaze, making the flames spread faster and burn more thoroughly.
Before their eyes, it wasn't just one or two Fire Slag Clusters; there were dozens, forming a terrifying fiery Hell.
