From publisher blurb:
Forbidden Spells of Incredible Power!
Everyone knows that there are some spells that are too dangerous, too wild, or just plain too powerful for any ambitious mage to cast. These rare, exotic, and above all forbidden spells are few and far between, but the immense opportunity that they provide to those who find a way to claim them is well worth the risks. And the risks are many: not only is there a risk that any practitioner who takes up such a spell will be hunted for dabbling in forbidden and “black” magic, but the spells themselves invite danger, and by casting them, the mage opens himself up for the possibility of losing control, and causing a terrible calamity.
Still, such forbidden magic is highly desirable to spellcasters of every sort, because despite all of that, or perhaps because of it, these spells contain more power than those of the average sorcerer or wizard. Destroy your enemies with powerful killing spells like power word massacre and damnation, or take up more defensive magic, like mirror of the witch, which surrounds the caster with nigh-impenetrable mirrors that protect her from all forms of attack. Alternatively, cast dance of demons, and laugh as your victims destroy themselves and each other by enacting a vrock’s dance of ruin. Strip virtually any target of spellcasting ability with demise of the warlock, or force your victims to kill themselves with proclamation of suicide.
The Book of Forbidden Magic includes 47 new spells with the forbidden descriptor. These spells are more powerful than traditional spells, but come with a drawback in the form of profane points, and the possibility that each time one is cast, they may cause a horrible calamity to befall the caster. The book also contains detailed rules governing profane points and calamities, including nearly 50 different specific types of potential calamities, from horrible magical backlash of various sorts to accidental planar rifts of all kinds and numerous sorts of mental intrusion by otherworldly entities. If you want spellcasting in your game to be more exciting, or are looking for more options for your character and enjoy taking risks and dabbling with powers man was not meant to know, look no further than The Book of Forbidden Magic.