This class is fairly powerful; it’s definitely an attempt to make a theurge actually keep up with the power of the (very powerful) expected entry classes. In particular, Perfect Inscription is quite dubious; it could potentially step on the toes of much-weaker classes, though I believe the increase in spell level will prevent that most of the time.

I’m going to include a few author’s notes/comments in the middle of this, by dropping out of the quote box. If they’re getting in your way, you can use the Edit History to see the version of this before I added them.

Artifex Goetia

Knowledge is power. Knowledge is magic, and ritual, and prayer, and power. As an artifex goetia, you have that fundamental knowledge: power is power. Form is of little concern, so long as you can command it. You’ll study dark grimoires, tomes of forbidden magic, artifacts locked away, deemed too dangerous for mortal minds. You’ll call upon the ancient ones, gods of mystery and eternity, and through the rites that bind and the lines that find, you will have them to do your bidding.

You may lay this power at the feet of your own divine patron, or claim it for yourself. The deeds wrought with this power may be great and they may be terrible. But all will be written down in your book, bound within its pages, to be read out and called upon at your need.

The fluff is pretty simple and straightforward, with a slight reference to Order of the Stick’s Xykon. It’s a little grimdark, but then the archivist is too, what with being from Heroes of Horror and having a class feature called Dark Knowledge. I explicitly and intentionally allowed the artifex to use these dark powers for the purposes of good, however.

By the way, the name is a reference to Ars Goetia, a section of The Lesser Key of Solomon, probably the most well-known occult book. It describes, or alleges to describe, how to summon and negotiate with 72 demons; these demons actually provided the names for the overwhelming majority of the vestiges from Tome of Magic, and Aleister Crowley’s edition provides the seals for all of the WotC-published vestiges (some of the online/Dragon vestiges use original seals).

Becoming an Artifex Goetia

To become an artifex goetia, you must be so adept at the arcane and sacred sigils that all magic can be reduced, for you, to diagrams and text, trapped inside a book.

Prerequisites:

• Ability to cast 1st-level arcane spells from a spellbook.
• Ability to cast 1st-level divine spells from a prayerbook.
• Ability to cast 2nd-level spells.
• Knowledge (arcana) 7 ranks, Knowledge (religion) 7 ranks.
• Knowledge Devotion feat, Scribe Scroll feat

I was torn on requiring Knowledge Devotion (and thus the Dark Knowledge (devotion) feature, below), since it’s a somewhat annoying to have yet another requirement on an already-difficult entry, plus it makes the class dependent on Complete Champion. I may come back to this and add an adaptation that doesn’s require it, especially if requested.

Otherwise, this is following the cue of the ultimate magus in allowing entry with only 1 level on one side. Unlike the ultimate magus, in this case it can be either side. So archivist 3/wizard 1 or archivist 1/wizard 3 is the expected entry.

Class Features of an Artifex Goetia

Level	BAB	Fort	Ref	Will	Special	Spellcasting
1st	+0	+0	+0	+2	Dark knowledge (devotion), read magic, secret page	+1 level of both
2nd	+1	+0	+0	+3	Familiar book	+1 level of lower-level
3rd	+1	+1	+1	+3	Lore mastery	+1 level of both
4th	+2	+1	+1	+4		+1 level of both
5th	+2	+1	+2	+4	Incorruptible study	+1 level of both
6th	+3	+2	+2	+5	Dark knowledge (vulnerability)	+1 level of both
7th	+3	+2	+2	+5		+1 level of both
8th	+4	+2	+2	+6	Bonus feat	+1 level of both
9th	+4	+3	+3	+6		+1 level of both
10th	+5	+3	+3	+7	Perfect inscription	+1 level of both

Weapon and Armor Proficiency—You gain no new proficiency in any weapons or armor.

Spellcasting—At each level except 2nd, your spellcasting improves as if you had gained a level in any class that casts arcane spells from a spellbook, and also gained a level in any class that casts divine spells from a prayerbook. Thus, your caster level and spells per day for these classes increase, and you may scribe any free spells that class would have gained. You do not, however, gain any other benefit that a level in either of these classes would have gained. If you have more than one class that casts arcane spells from a spellbook, or more than one class that casts divine spells from a prayerbook, you must choose one for each category.

At 2nd level, however, you gain these benefits from only one category, arcane or divine. If you can cast higher-level arcane spells than you can divine spells, your divine spellcasting improves as above. If you cast higher-level divine spells than arcane spells, your arcane spellcasting improves as above. If your highest spell levels are the same for both arcane and divine spellcasting, your spellcasting in the class with the lowest caster level improves as above. If the caster levels are equal too, then you may choose arcane or divine.

Again, another cue from the ultimate magus, on losing another level in-class. I made the rules for judging “lowest level” a harder to dodge, because I think this class is a bit more powerful than ultimate magus. I don’t lose more levels, though, because without the tricks that let you control which side ultimate magus advances, losing more levels would be very painful.

Dark Knowledge—Your class level stacks with archivist class levels for the purpose of the number of times per day you may use Dark Knowledge. If you have no archivist levels, simply use your class level for this purpose (i.e. 3/day + 1/day for every three class levels).

Devotion—You share your devotion to knowledge with an ally, allowing that ally to better understand their foes’ intentions. One ally gains your bonuses from Knowledge Devotion for the affected creatures for one round. If you succeed on the check by 10 or more, you may grant these bonuses to two allies, or you may grant them to one ally for two rounds. If you succeed on the check for 20 or more, you may grant the bonus to three allies, or to one ally for three rounds, or to one ally for two rounds and to two other allies for one round.

Vulnerability—You indicate the vulnerabilities of your foes, allowing your allies to ignore some of their defenses. Your allies within 60 ft. treat all saving throw DCs as being having a +1 bonus when affecting the identified creatures, and they ignore any damage reduction, regeneration, or spell resistance the target may have had (but not the spell immunity of, for example, golems). These benefits last for three rounds.

Read Magic ^Su—You are continuously under the effects of read magic, allowing you to always read magic spells.

Secret Page—You may prepare the secret page spell, as a 3rd-level spell, without needing to have it written down ahead of time. This works the same as a wizard preparing the read magic spell. You may do so with any class you have capable of preparing 3rd-level spells.

Familiar Book—Using magic similar to that which binds a familiar, you can craft special books similar to a prayerbook or spellbook. To do so, you need a spellbook or prayerbook, plus 6,000 gp worth of other materials. The process takes seven days, working eight hours a day, and requires the expenditure of a prepared secret page spell each day you work on the book. The seven days need not be consecutive. This is an item-creation process.

The familiar book becomes an intelligent item that actively protects the spells you have found and scribed within it. It contains any spells that the book you started with contained, and you can scribe arcane or divine spells within the familiar book. It counts as both a prayerbook and a spellbook for any effect that cares. See The Artifex Goetia’s Familiar Book, below, for more information.

You may create multiple familiar books, and you may create a familiar book even if you already have a familiar.

Lore Mastery ^Ex—At 3rd level, you gain a +2 bonus to Decipher Script checks and to the checks of any one Knowledge skill. These bonuses do not stack with any bonuses due to the Lore Mastery feature of other classes; instead, choose a new Knowledge skill to apply the bonus to.

Incorruptible Study—As a 5th-level artifex goetia, you are never trigger the effects of magic, curses, and so on that are triggered by reading. Thus, for example, you are immune to the effects of a glyph of warding, sepia snake sigil, or symbol of insanity. You do not trigger explosive runes, but if someone else does while you are within range, you are damaged by the blast. You furthermore are never corrupted, tainted, or driven mad by what you read or learn; knowledge can never hurt you.

Bonus Feat—At 8th level, you gain a bonus feat. This feat may be any one that an archivist or wizard could have chosen as a bonus feat.

Perfect Inscription—You may write down any sort of magic you come across, no matter how unusual, and then prepare it as a spell.

• If the magic is a spell that you could normally scribe, you scribe it as normal and this class feature has no effect.

• If the magic is a spell that you couldn’t normally scribe (including divine spells you could scribe as arcane or arcane spells you could scribe as divine), but is still arcane or divine in origin, you scribe it as an arcane or divine spell, as appropriate. If it is neither arcane nor divine, you can scribe it such that it may be prepared by either your arcane spellcasting class or your divine spellcasting class.

• If the magic is not a spell, but is divided into levels like spells (e.g. infusions, maneuvers, mysteries, vestiges), you may treat it as a spell that is neither arcane nor divine.

• The magic’s spell level, regardless of whether or not it is actually a spell, is its level for the class you are getting it from, plus 10 − the highest level of magic that class is capable of. Thus, a 3rd-level bard spell (assuming you are not a bard) would count as a 7th-level spell for you (bards have a maximum of 6th-level spells, so 10 − 6 is 4, plus 3 for a 3rd-level spell).

• You use the caster level of the spellcasting class in whose spell slot you have prepared the magic as the level (meldshaping level, effective binder level, initiator level, etc.) used for the effect.

• In all cases, there are two ways of scribing: from a source in which the spell has been transcribed, like a scroll, or from a practitioner who can use the magic in question, who must work with you during the scribing process. Many magics cannot be written down, however, leaving only the latter option.

• Particular forms of magic have special rules, as follows:

  • Expanded Psionics Handbook

    • When you “cast” psionic powers from a spell slot higher than the minimum you need, it is augmented by 2 power points for every spell level higher than the minimum.

  • Tome of Magic

    • Vestige pacts prepared as spells may be “cast” by going through the usual pact-making process. They only last for 10 minutes per level once the ritual is complete, however, and you may have only one pact prepared at a time.

    • You do not ever treat mysteries as spell-like or supernatural abilities; you always cast them as spells.

    • You do not gain any free or bonus ranks in Truenaming, so most utterances are of minimal use to you unless you specifically take ranks in it.

  • Tome of Battle

    • Martial maneuvers you prepare are “cast” as if the prepared maneuver were a martial script of the maneuver. You may prepare multiple copies of the same maneuver, but you cannot activate it more than once in the same encounter.

  • Magic of Incarnum

    • When you prepare a soulmeld as a spell, you must choose which chakra it is prepared for. Merely preparing it causes it to occupy that chakra, just the same as if you had shaped (but not bound) a soulmeld there. This means you cannot prepare two soulmelds for the same chakra, though you may prepare multiple copies of the same soulmeld.
      • Casting the soulmeld causes it to be shaped to its chakra, granting its basic effect and allowing you to invest essentia in it, for 1 minute.
      • The soulmeld can be bound to its chakra for the same minute so long as it is cast from a spell slot of sufficient level, as follows: 2nd: Crown, 3rd: Hands or Feet, 5th: Arms, Brow, or Shoulders, 7th: Throat or Waist, 9th: Heart. You cannot bind it if you have a magic item in that slot.

This feature concerns me. It gives you access to a ton of effects, and potentially allows you to render other classes, already weaker than archivist or wizard, fairly pointless as you get to steal their few unique tricks. Still, the large increase in effective spell level, and various other limitations, will hopefully make this a much more difficult feature to use, one that sees more application on a fluff level than power level.

The Artifex Goetia’s Familiar Book

A familiar book is an intelligent item. It behaves as a blessed book for the purposes of inscribing spells within. It has HP equal to its master, hardness equal to 5× its master’s artifex goetia class level, and resistance to all energy damage equal to 3× its master’s artifex goetia class level. It also gains more benefits based on its master’s artifex goetia class level.

Level	Int	Wis	Communication	Capabilities	Senses
2nd	13	13	Empathy¹	Secret page	60 ft. vision and hearing
3rd	13	13	Empathy¹		60 ft. vision and hearing
4th	14	14	Speech²	Remote viewing	120 ft. vision and hearing
5th	15	15	Speech²		60 ft. darkvision and hearing
6th	16	16	Speech²	Shared notes	60 ft. darkvision and hearing
7th	16	16	Speech²		60 ft. darkvision and hearing
8th	17	17	Speech, telepathy³	Indestructable	120 ft. darkvision and hearing
9th	18	18	Speech, telepathy³ ⁴		120 ft. darkvision, blindsense, and hearing
10th	19	19	Speech, telepathy³ ⁴	Return	120 ft. darkvision, blindsense, and hearing

1. _{The possessor feels urges and sometimes emotions from the item that encourage or discourage certain courses of action.}

2. _{Like a character, an intelligent item speaks Common plus one language per point of Intelligence bonus, and can read any languages it can speak. It can communicate telepathically with its master.}

3. _{The item can use either communication mode at will, with language use as any speaking item. It can communicate telepathically with the wielder.}

4. _{The item can read all languages as well as use read magic.}

This stuff comes straight from the intelligent item rules, aside from the capabilities.

Secret Page ^Su—The familiar book automatically uses secret page, as the spell, to hide the magic contained within it from anyone but its master.

Remote Viewing ^Su—The familiar book’s master may, at will, concentrate and view the book’s surroundings, seeing whatever the book can sense. This may be done at any range, and for as long as the master continues to concentrate, provided the master and the book are on the same plane. This is a scrying effect.

Shared Notes ^Su—Using any of his familiar books, the master may prepare any spell inscribed in any other familiar book he has created that still exists. For each spell not in the familiar books he has before him, however, spell preparation takes an additional 10 minutes per level of the spell.

This seems kind of awkward; I’m considering changing it so that you have only one familiar book, but it has infinite pages. Thoughts on that would be appreciated.

Indestructable—At this point, a familiar book is astoundingly difficult to destroy. Only effects capable of destroying a major artifact can destroy the familiar book.

This... is not as great a description as I’d like it to be. The description of major artifacts says that each major artifact should have a single, specific way to destroy it; the familiar book does not. That said, certain powerful spells do give ways to destroy artifacts, which is what I’m going for here. It would take a lot to get a 17th-level wizard to cast disjunction on the book, particularly considering the tempting possibility that one could convince the book to allow him to use the power contained therein.

Return ^Su—At will, as a standard action, the familiar book’s master may call it to him. This is a Conjuration (calling) effect, and works at any disatance and even across planes.

This book is way too important to allow it to be trivially taken. Calling effects can be blocked, but at least this requires that someone who steals the book get it to a location that blocks them before the wizard notices it missing.

This is a known tendency of 3.5...

As KRyan correctly points out in his answer, to a certain extent this is just the way 3.5 is. There are many options available to players (Save-or-Die/Save-or-Lose/No-Save-Just-Lose spells, ridiculous amounts of damage like you've seen with your Barbarian PC, etc.) that instantly remove enemies from an encounter.

There aren't a whole lot of options for "soft" defense - there are immunities, there are things like immediate actions that protect you from a given attack, but there aren't a lot of good ways available to players to reduce the impact of incoming attacks (many of the best spells are strictly all-or-nothing; Damage Reduction doesn't scale well enough to be an effective protection, etc.).

Put those two things together, and you get what's often called rocket tag - the two sides trade blows that will end the fight if they land, they do their best to prevent enemy blows from landing, and whoever [fails a save/isn't immune to something/takes a full attack/etc.] first loses.

...but it can be mitigated somewhat, by picking options for your enemies that aren't available/optimal for PCs.

The best way I've found to mitigate this issue is to make enemies who are better at taking/preventing damage and other fight-enders than they are at ending fights. This requires building your enemies much differently than you would if you were building them to be effective PCs. Some tips for this approach:

• Make your enemies immune or highly resistant to the standard encounter-enders. Sufficiently high saves prevent save-or-lose spells from being reliable, but if you want to be sure to prevent rocket tag, you may also want to layer on effects like Death Ward, Freedom of Movement, etc.
• Give your enemies lots of HP. As KRyan says, this isn't enough on its own (it just incentivizes your players to use attacks that don't deal HP damage), but combined with defenses against non-damage attacks, it can result in more uptime in fights.
• Give your enemies immediate action defenses, Contingencies, etc. One-shotting an enemy isn't a very satisfying fight outcome. Using your first one-shot move, having it countered by something like Celerity (SpC), then having your party member use a second powerful attack that lands because you've already burned through the enemy's defenses? Feels more like you've accomplished something, and less like you've trivialized the encounter.
• Have your enemies use lots of attacks that work over time, but not very many encounter-enders. Save-or-suck spells like Bestow Curse, damage-over-time effects like Power Word: Pain (RotD) or Freezing Fog (SpC), battlefield control like Web, grappling opponents (if your PCs aren't immune)...these are all strong options that make the PCs feel like Bad Stuff™ is happening to them, without instantly knocking them out of the encounter entirely.
• Use the terrain to make it harder for your PCs to land encounter-enders. If a competently built pouncing Barbarian lands a full attack on pretty much anything, that thing is going to die. So place obstacles that make it hard for the Barbarian to charge, use enemies that fly if your PCs have trouble with that, use incorporeal enemies that move in and out of walls to force your PCs to use readied action attacks, etc.

But isn't this unfair to PCs who specialize in the options I'm hard-countering?

If you just drop it on your PCs with no warning in a game where they've gotten used to normal enemies, yes.

The reason 3.5 has a tendency toward rocket tag is that PCs (and enemies who work roughly like PCs) are much more effective if they build toward offense than defense. In order to counter this tendency, you have to use enemies who don't work like PCs - enemies who have strong defenses that aren't available to PCs, but at the same time don't use some of the most effective offensive options that PCs do.

This may interfere with your players' enjoyment of the game:

• If they expect enemies to be playing by essentially the same rules they are, then the fact that those enemies are immune to lots of their attacks may strike them as unfair - "If that monster's magically immune this stuff, how come I can't be?" or "I spent all these character resources investing in high save DCs for my spells, and now you're telling me the big bad is immune to everything?"
• ...and the fact that their allegedly powerful enemies don't just kill them with encounter-ending spells that they aren't immune to might ruin their suspension of disbelief - "The evil wizard forced me to tromp through his tower full of Freezing Fog fighting skeletons before getting to him. And it was a cool fight, but Freezing Fog is a 6th level spell. If he could cast 6th level spells, why didn't he just nail me with Irresistable Dance on the first round and call it a day?"

But at the same time, you're the DM. Your enemies don't have to be built using the same toolkit that's available to the players, and there's no rule that says they have to have the same capabilities, or be vulnerable to the same forms of attack.

So, talk to your players! See which is more important to an enjoyable gaming experience for your group: enemies who play by the rules, or fights that last longer than three rounds? If you have players who feel they would be unfairly affected by these sorts of changes (e.g., a Beguiler who will be useless if all important enemies are immune to [mind-affecting] stuff), see if they would be okay with being allowed to rebuild their characters to take them into account, or if they prefer the game in its current form.

Then decide how much of this encounter redesign you want to do, with your players' needs and preferences in mind.

What can your players do?

Finally, to address your last question about what your players can do to mitigate this: nothing, unless you change how their enemies work.

The reason 3.5 tends toward rocket tag is that offensive options are stronger than defensive options in the default game. Thus, the best way for PCs to keep themselves alive is usually to take enemies out of the encounter as quickly as possible. From your question, it sounds like your players are already doing this.

If you want to make defensive options viable for them, you have to change the challenges they face - make it so that taking enemies out of the fight quickly is impossible, and then it's no longer the best way to stay alive. Make it so that enemies use damage-over-time effects or debuffs instead of deadly finishing moves, and healing/defensive buffs (besides the ones that provide immunity to encounter-enders) become stronger.

Your players are already doing the right stuff to stay alive in the kind of game they're in. If you want them to behave differently, you have to change their incentives.