Inferno is a demonic spell that engulfs the target in flames.
An inferno starts as a ball of flames in the demon's hand (or paw) and moves rapidly to the target, then engulfs them in flames. It is slightly less destructive than a Detonation, but because other objects catch fire has a greater area of effect. Infernos don't possess a particular colour, but vary with the spirit using them. Bartimaeus for instance, is usually seen to use blue fire, where as other have used green, orange, and red.
Infernos are weak against being with Earth-based magic, such as Golems.
As beings of air and fire, djinn commonly use these attacks. Afrits, as fire spirits, use them just as much. It is unknown if marids use them as frequently, if at all. Lesser demons are not recorded as using them.