Unholy Magic is the magic of Demons and Demonesses, of which there are many. They are pure, perfect beings of darkness and evil, and all true Unholy Clerics should aspire to be as close to Demonly as possible. This is easier outside the temple than in.
The Demons and Demonesses are busy with their own affairs and pay little attention to mortal cares. So if you're an overgrown Boy Scout (not that there ARE Boy Scouts in this world...), you can still be an Unholy Cleric. You just can't cast any Holy spells. Gods and Demons alike will notice if someone switches sides, and will not be pleased. To get back in the Demons' "good" graces after being purified takes a hell of a lot of corrupting, and usually requires you stick around the temple for quite some time, to prove your devotion and remove you from temptation to fall again. Even then, expect to be watched by others of your order.
Still, there are perks to being an Unholy Cleric, i.e. the ability to cast those who displease you into Damnation and Perdition for all eternity. Unholy Clerics usually have a reason for wanting the generally destructive powers of demonkind on their side, but it's not necessary. You could just like blowing $#!% up.
Unholy Clerics are somewhat more likely than their Holy counterpoints to take up other magic schools, as they generally LIKE having more and more power.
A vested Cleric/Priest/Priestess (one who has graduated from an unholy temple; the term "cleric" is used for a priest/priestess who is not living in a temple - either wandering, or living on their own) is Level 4; Levels 1-3 are the still-learning stages of neophyte, apprentice, and journeyman (respectively). Levels 5-8 are simply progressions and bring with them no change in rank on their own (although temples may promote/demote at their discretion). Level 9 is High Priest, and Level 10 is Unholy Master. The difference is that High Priests are generally in charge of a temple, maybe overseeing two or three if they're close together. Unholy Masters are more likely to be hermits or wandering chaos-makers. Even a Level 1 neophyte can still see a black sort of "glow" outlining Unholy or Cursed objects or people, but cannot detect the "aura" or "glow" of other magic types unless they've also studied those. The "glow" is not visible on oneself unless one is actively working magic at the time, and fades when the spell is cast or otherwise ends.
As with most magic schools, you buy your Level of magic with points. In the case of Holy/Unholy spells, your level decides what spells you know and what strength those spells are. Buying level 1 costs 6 points, level 2 costs 5, levels 3 - 8 cost 4 points each, level 9 takes 5 points and level 10 takes 6 again. Keep in mind that if you take Unholy Magic, you CANNOT take Holy Magic.
.:Unholy Spells Alphabetically:.
.:Unholy Spells by Level:.