Hello, posters, lurkers, and general readership!
Some recent free time, and the potential of joining a game with an experienced GM and novice players (low optimisation curve ho!) lead me to cogitate on that ancient, once heavily played[1], prestige class that is the Mystic Theurge (MT). Attempting to supplement such thoughts as I contemplating bringing one to a relaxed campaign obviously meant visiting the internet. Whereupon I found endless discussions on how bad it is. Never play one type insistence in some cases. To which I disagree after more thought, and some test scenario playing.
I am making all this contention to address my own thoughts, to hopefully reassure other players their concept can work, and to (also hopefully) inspire someone to try it out for a campaign.
Now, whilst it is utterly beyond contending that the MT is weaker than 9th level casters, I found myself wondering what could actually be done playing one. What is it capable of providing to a given party?
Firstly, the rigmarole that sets the ground rules: Presumably we're all aware of the prestige class: 2nd level Arcane and Divine casting to enter, boosts both of these every level, the ability to prepare X side spells by use of higher slots from Y side, and a capstone that lets you break the action economy...once per day. In addition, I am assuming an audience with at least a casual knowledge of both "The Forge of Combat" and the tier system, see a pathfinder analysis here. Agreement philosophically with these is not what I aim to discuss, or particular details. It's just a framework to operate in. Holding ideas on what a competent party might look like, and a stratification of what characters can and can't do, respectively. Further, this conversation will be thoroughly about the game as presented, and as a game. I.e. With some conception of "winning", vague as the concept may be. Winning in roleplaying games is difficult to define. In an attempt, I proffer: Tangibly and regularly contributing to a party's success in completing a campaign by operation within the rule set. It's a weak definition, and I fully accept constructive attacks on it to come. The forge of combat discussion also holds a definition but that one centers on combat encounters.
Secondly, a thought experiment; consider a class exists which offers 2/3 casting from the wizard/sorcerer list and a series of SLAs that mimic the cleric/oracle list at a similar rate of progression (of course, class features a 3/3/10 build would obtain are also mimic'ed). For the purpose of closest approxmiation, we may also insist such a class has 1/2 BAB and d6 HD.
I see the complaint that we're talking of a MAD creature while we're at this. I don't feel this is an enormous problem. The Arcanist, Cleric, Shaman hardly are broken by needing two mental ability scores to fully explore. With respect to the channel from a few levels of cleric (if you go such a route (it is the best divine spell list so plausibly)), I really fail to imagine neglecting charisma will create much pain for you.
I appreciate the above holds some discrepancy in early levels, but it seemed the quickest generalisation for the following point, which is to observe the highest spell accessed at a given level. This is done below under the premise of a player going Wizard 3/Cleric 3/Mystic Theurge 10.
L__P__S__2/3__MT
1__1__1___1___1*
2__1__1___1___1*
3__2__1___1___2^
4__2__2___2___2*
5__3__2___2___2*
6__3__3___2___2*
7__4__3___3___2_N
8__4__4___3___3*
9__5__4___3___3*
10_5__5___4___4*
11_6__5___4___4*
12_6__6___4___5^
13_7__6___5___5*
14_7__7___5___6^
15_8__7___5___6^
16_8__8___6___7^
For clarity's sake: L = Level, P = Prepared (full caster, i.e. Wizard), S = Spontaneous (full caster also, i.e. Oracle), 2/3 = 2/3 casters (i.e. Magus, Inquisitor, Bard), MT = Mystic Theurge build. I have denoted with an asterisk * levels at which our build has the same spell access as a 2/3 caster. Particularly our theoretical 2/3 caster (see above), levels the MT build accesses higher level spells with a caret ^, and levels the MT build falls below with an N. I do not consider above 16th level because I find generally, this is analysis for play seen by a very small percentage of players. 16th neatly covers most adventure paths anyway, useful if we attempt to discuss campaigns - as we can hold a shared context.
Some observations come out of this: 1. That the MT build matches a 2/3 caster for 10/16 levels. If we focused on PFS play: 9/12. 2. It begins to outstrip the 2/3 caster levels 14-16. Arguably 12-16. Though that the build works well at this point is rarely in contention aside complaints that the straight full casters are ahead.
This analysis may be repeated for Prepared/Spontaneous entry, or sponstaneous/spontaneous entry - but it is rapidly apparent above how many levels would earn the marker "N", thus I think we can ignore it as being even more terrible in optimization terms. Less ignorable is going prepared/prepared 1/3/2/10 or similar - which is not inconcievable, and does make the similarity more acute.
Before I continue, I reiterate: That a straight full caster build is almost invariably stronger, and this is not in contention, I write simply to ask what a forward-looking player might expect playing such a build. Obviously, our theoretical single-class theurge doesn't exist in the rules. What do however, are other 2/3 casters. From which I begin to find argument to support the play. For one, the wizard/sorcerer list is better than any of the 2/3 caster classes'. Given tier system treatments generally put these on 3, I find a strong point to refute the overall impression I felt people had, that the mystic theurge is unless. I do not feel this is true.
Now, our thought experiment monstrosity is hardly comparable to an inqisitor, magus, warpriest (and similar) due to the fact these classes are set up to be quasi-martial characters. The summoner doesn't really compare due to being better than full casters at full casters' best trick (the dick). With regards to the warpriest, it is simple to make a very direct comparison: Would we consider a warpriest archetype that traded out all features to toss out wizard spells, with accompanying extra spell slots good? I'd posit so.
Anyway, the best approximation I can see is perhaps a casting focused Bard. It is this I would like to consider the role of an MT fitting. Sure, you lack all those skill monkeying boosts of the Bard. But last I checked, a great issue in the system was low-level spells replace skills. Stealth? Vanish, invisibility, so on. Bluff? Glibness. Climb? Spider climb. I may go on, but I am already being somewhat facile here. "But performance!" you may cry. I have you covered: You have more buffing spells. Bless for one. This is not to say the bard is not effective at these things, merely to draw a comparison which mainly ends to note a casting focused bard contributes mostly in the roles of "arm" or maybe "anvil". Both of which the MT can fulfil.
In terms of being an anvil, I'm lead to deal with saves. A straight full caster has better saves but the best battlefield control spells do not rely on saves for efficacy. Web creates difficult terrain regardless of save. Obscuring mist blocks vision, no save. A straight full caster may have better tricks, but it's hardly like you have none. As to blasting - yeah, that isn't in the ballpark here. You're facing 5-10% less efficacy in this department, on rough analysis.
On the anvil competence, and as a damage source however, I turn to one thing the MT excels at: Necromancy. Assuming the traight Magical Knack is in play on one side, you match and then outstrip the Juju mystery oracle at level 8 for sheer Undead HD you can control. You've dedicated all your time to magic, why should you do any actual lifting?
Annoyingly, this is just after the most glaringly annoying spot in the whole build: 7. All I can genuinely offer a player considering playing an MT at this point is to pay and wait your way through. Scrolls, wands, etc. Look, you're just awful. At amusingly, the point you actually begin the very thing you're trying to do. Not that Eldritch Knight makes me see a pattern of this across prestige classes but... Still, the contention it's a bad build is most acute here because you are bad at your role here. However, things get better, and are ameliorated by prep.
Admittedly, a point stands to which I lack a response on discussing the classic cleric/wizard build which is "what does X side bring the other glaringly lacks?"
This ramble so far is all I have time for but I will hopefully get back to this. Obviously, feel free to reply to what's here so far. If I'm talking crap, call me out on it. :)
[1]This reminds me: I do not care to discuss a particular FAQ as its present status is one of houserules. It is not within the baseline expectation of experience.