Infernal Magic

Infernal Magic is a secondary school under Exomagic that includes magic schools that originate in supernatural beings that are neither monotheistic gods whose magic is tailored so that it deals damage to evil beings, nor Aberrants. Unlike Divine Magic, however, it is more malevolent. It oftens hails from the 'opponent' sides in monotheism religions. It causes no sanity damage, however.
In short, its damages aren't dependant on target's ammount of sins, and aren't causing sanity damage to its users. Because of its nature, there is no baseline Infernal Magic (with exception of certain theurgies that aren't aligned with the rest of magic schools).

Subschools of Infernal Magic

Destruction Magic [HX] - A tertiary school of Infernal Magic that can be learned only in Valley of Ashes, believed to be connected with Destroyer. It causes terrifying bodily damage - with targets fingers simultaneously breaking, nails suddenly ripped out, or even things like the target suddenly lifted from the ground and then rammed into the ground or impaled on something/vivisected in most gruesome manner.
Additionally it causes debuffs similar to Death Magic and Mind Magic. Making it a particularly devastating type of offensive magic.
Depths Magic [HX] - A tertiary school of Infernal Magic that can be learned only in Valley of Ashes, believed to be connected with Destroyer. It can be easily discerned by navyblue colour effect, the feeling of drowning it causes to the onlookers and those debuffed or hit by its hexes, and the strenghtened effect of Death Magic - meaning sapping out lifeforce.
It also causes an emotional drop into general depression and dark vision of the world, while simultaneously causing a sort of mania that makes the onlookers think that the caster is actually enjoying this whole darkness that swallows them.
Ashen Magic [HX] - A tertiary school of Infernal Magic that can be learned only in Valley of Ashes, believed to be connected with Destroyer. It has no directly offensive skills, instead having many non-daemonic servants made from certain types of darkened ashes (that can, in a way, 'possess' bodies, changing them into some sort of ashen-like zombie).
The effect on mentality of onlookers is abysmal. However, it tends to cause mental darkness to swallow the mind of the caster, leading to self-mutilations or even maniacal attempts to burn himself alive. It only barely avoided being added to Profane Magic.
Terror Magic [HX] - A tertiary school of Infernal Magic that hails from a place known as Six Mines in a Needle Mountains, considered a terrifying place even amongst magical anomalies, a place when your own hallucinations can shred you to pieces in a most physical and material way possible. It is sometimes considered an ancient predecessor of Nightmare Magic.
Terror Magic can be described as third tier of illusive-like magic, this most dark. 'Illusions' of Terror Magic are so terrifying they can damage minds simply by being seen. What's more they can to a point damage physically, by perfectly 'mimicing' touch. Side effect being a high rate of heart attacks, insanities and braindeaths among users of Terror Magic - but one not connected with Aberrant effects, making the nature of this magic very dubious. Which makes this magic be on a very edge of purging.
Dissolution Magic [HX] - A tertiary school of Infernal Magic, that hails from anomaly known as Gray Valley in Iron Mountains. According to tales of local people, a star once fallen there. According to magicians and scientists, a very weird meteor once fallen there. An effect is both anomaly and a type of magic, slightly similar to Death Magic.
The difference is a generally gray coloristic (tinted with some very strange illuminations) and a variety of of debuffs similar to Death Magic. That, however, culminate with the victim ending as a stain of gray (and still living) organic matter. They also tend to be much more costly in terms of power, while damaging caster's mind. There are suspicions that said meteor originates from the Void, making it something connected to Profane Magic.
Chaos Magic [HX][P] - A tertiary school of Infernal Magic that hails from darker parts of diretian religion, mainly from the forces of Chaos.Which includes a vast number of Chaos Lords, archdaemons whose sole reason for existence is tormenting and destroying mortals in any way possible. Magic that hails from them is an... interesting one.
Most of its hexes are roughly based on elemental magics, just... twisted into much darker forms. For example a chaos fireball will have a deeply crimson colour, and burn noticably weaker (killing targets slower) while simultaneously causing debilitating mental damage with many unique debuffs. This magic also seems to prefer sentient targets, causing increased mental damaged to them.
There were also spells that could modify bodies and souls of living beings, changing them into horrible, body horror-type abominations servile to their creator. Not to mention being able to quickly break minds. Imperium - together with Diretian leadership - managed to mostly purge it from the world. While it still exists (for example in the hands of Chaos Lords) it is still hunted and proscribed in Imperium.
Blackfire Magic [HX] - Blackfire Magic is a much darker cousing of @Fire Magic, believed to descend from darker part of visenian theology, namely Svarov and his archdaemonic underlings. Some of them throw or spit fire in dark colour, described as immensely powerful. Some magician tried to replicate it... and achieved that, creating Blackfire Magic.
Black flames burn using mana rather than air. They are extremely hard to be put down, and you can set even water or stone on fire. While the physical damages are abysmal, it burns magic power and life force, causing growing weakness and, soon, complete paralysis and death through Death Magic-like effect.