Comments from the Finger: This one is a favorite among 3.5 optimization groups. Back in the day, it was a prestige class that gave you a new level of divine spells every time you took a level in the class -- which is still completely unprecedented. To give some context to how immensely broken this was, a DM of mine used to allow literally anything from any book in 3.5, except for this and Horizon Walker. It was my envy in the 3.5 days, and I'm still in love with the theme today.
Ur priests are scarcely clerics in the traditional sense; many even despise the gods. Rather than being granted divine magic and authority by a deity or powerful idea, clerics of the Ur Domain siphon off the energies granted by gods to divine spellcasters, using it for their own needs without giving even lip-service to any god. Ur Priests can come from any walk of life, but the most dangerous are always ex-clerics and paladins who have abandoned their gods. They violently oppose religion in any form, and use their powers to weaken the gods and destroy their followers.
Ur Domain Spells
Starting at 1st level, when you prepare spells following a long rest, you can select one spell to prepare from any list of cleric domain spells, and it doesn’t count against the number of spells you can prepare each day. This spell must be of a level for which you have spell slots. At 8th level, you may prepare 2 spells in this way, and at 17th level, you may prepare 3.
At 1st level, you have advantage on saves against divine spells, which are spells cast by clerics, paladins, druids, rangers, and other sources the DM deems appropriate.
Channel Divinity: Anti-heal
By 3rd level, as a bonus action on your turn, you can use your Channel Divinity to invert positive energy auras around you. For 1 minute, no creature within 60 feet of you can regain hit points due to magic. Instead, when a creature would regain hit points, it must make a Constitution saving throw or take necrotic damage equal to the amount it would have regained.
Starting at 6th level, you can expend two spell slots of the same level to cast a spell that you know of 1 level higher.
Starting at 8th level, you add your Wisdom modifier to the damage you deal with any cleric cantrip.
By 17th level, you have learned to siphon magic from spellcasters just as you do from the gods. As a reaction when you affected by a spell, you can learn it as a cleric spell and prepare it until you complete a long rest. You can only learn one spell in this fashion at a time and it does not count against the number of spells you can prepare. If you attempt to learn a new spell after you have learned one with this feature, you immediately forget the old spell.
Changelog: 4/23/15: Anti-Heal: Creatures must make a save, damage is equal to hit points that would have been regained.
Steal Magic: Spells are prepared, in addition to being learned.
4/24/16: Ur Domain Spells: Reworded
12/22/16: Anti-Heal: Wording fixed