The Agilomancer (3.5e Optimized Character Build)
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Ever wanted to see what what happen when you have a Dex Based Spellcaster? Want to be a Spontaneous Mystic Theurge at Level 6? It's rather simple, to be sure. But you've got your bases covered. That's right. Arcane and Divine Spellcasting. It's Easy. I've planned your progression until 6th Level. Take all ten levels of MT. At that point, You can go epic Mystic Theurge, but I wouldn't suggest it (unless you've got a sane DM who will scrap the Epic MT spell progression and use the normal one.) The Character sacrifices Higher Spell DC's for Improved Armor Class, Attack Rolls, and Certain Skill Checks.
There's also an alternate, Non-Spontaneous Build below.
Mystic Theurge- Core Sorcerer- Core Shugenja- Complete Divine Swashbuckler- Complete Warrior Illumian/Illumian Feats- Races of Destiny
 Game Rule Components
For this, we'll be using 32 point buy, because it's simple.
You NEED Precocious Apprentice at Level 1. It's a requirement. Now, as for other feats, you're going to need to take some flaws. Which is completely fine. If you want to be a total wanker, take Meager Fortitude, and when you snap out that Necropolitan, you're golden. Feat for Free anyone?
Dex Boosting Gear is Win. Gloves of Dexterity of the best quality you can get. Cha Boosting gear is your next best bet.
Starting Ability Scores (Before Racial Adjustments): 9 str, 18 Dex, 3 Con, 12 Int, 18 Cha
Race (Templates): Illumian is a REQUIREMENT of this build. Necropolitan is a great one to take as well, as it's a no-level adjustment template that gets rid of your need for Con and makes CHA your Concentration Skill.
Starting Racial Traits: As it's not SRD, I'm not sure if I can really list them here. Look on Page 53 of Races of Destiny. But I can tell you that you need to take Krau as your primary sigil and Uur as your secondary sigil. Giving you the almighty UurKrau Sigil. :P
|Saving Throws||Feats|| Class
|1st||Sorcerer1||+0||+0||+0||+2||Combat Casting, Precocious Apprentice, Weapon Finesse||And So it Begins.||Put 4 ranks in Knowledge Arcana|
|2nd||Src1/Shugenja1||+0||+0||+0||+4||-||Spellcasting||Boost Knowledge Arcana by 1. It's Necessity.|
|3rd||Src1/Shu2||+1||+0||+0||+5||Feel Free to Grab some sort of Sigil Feat, or better yet, something metamagic.||Boost Knowledge Religion and Knowledge Arcana to 6||This is where you Get that Necropolitan Template. Your crappy hit points are now d12's and aren't subject to that disgusting 3 in your con.|
|4th||Src1/Shu3||+1||+1||+1||+5||-||Boost that Dex Score!|
|5th||Src1/Shu4||+1||+2||+0||+6||-||Your First REAL set of Level 2 Spells. Aren't you happy?|
|6th||Src1/Shu4/Mystic Theurge1||+1||+2||+0||+6||Whatever you Like||--||And there you have it.|
 Other Components
You're going to want to dump all but one of your ability boosts into your dex. Your Final Ability Boost should be dropped into Charisma so you can get access to those tasty 9th level spells. Depending on your DM, when you hit level 15, You've reached a crossroads. If he allows you to use Normal Mystic Theurge Spell Progression past 10 (why he wouldn't is beyond me.) Then continue with Mystic Theurge. If you've decided that you Really Really Really want to cast better arcane spells, you could pick up levels in an Arcane Prestige Class, or drop a few more levels in Sorcerer. There are ways to boost your spellcasting abilities on both sides even farther, but they REQUIRE you to be some sort of prepared caster on either side. We'll get to that in a minute. As for Spontaneous casters, this is a viable build, to be sure.
Because it does. There's the argument over whether or not Precocious Apprentice works. To be blunt. It does. It grants you the ability to cast a level 2 spell. Which meets the entry requirement of the prestige class. Some will say you need to be able to cast Level 2 Spells, in the plural. But can a level 4 Sorcerer only cast one level 2 spell? Should their entry to MT be delayed by ANOTHER level? I didn't think so.
This is Character Optimization. It's about RAW, not RAI.
 Munchkin-Size Me
Use the Prepared Caster Variant. It's better, but in a different way.
 Side Notes
The Strength of this build lies in it's ability to Simply Cast what it needs, rather than prepare those spells ahead of time. With your dual casting, you can select versatile spells from both lists in order to make up for your shortcomings.
Lack of spells, I suppose. The sigil only allows you to use your dexterity to add bonus spells, not the spell DCs.
 DM Counters
Anti-Magic Field. :'(
 Prepared Casting Build
Same As Before, Illumian with UurKrau Sigil. Only this time we're using the Archivist/Wizard. So we'll be hitting Mystic Theurge at Level 5 rather than Level 6.
|Saving Throws||Feats|| Class
|1st||Wizard1||+0||+0||+0||+2||Combat Casting, Precocious Apprentice, Weapon Finesse||And So it Begins.||Put 4 ranks in Knowledge Arcana|
|2nd||Wiz1/Archivist1||+0||+0||+0||+4||-||Spellcasting||Boost Knowledge Arcana by 1. It's Necessity.|
|3rd||Wiz1/Arc2||+1||+0||+0||+5||Feel Free to Grab some sort of Sigil Feat, or better yet, something metamagic.||Boost Knowledge Religion and Knowledge Arcana to 6||This is where you Get that Necropolitan Template. Your crappy hit points are now d12's and aren't subject to that disgusting 3 in your con.|
|4th||Wiz1/Arc3||+1||+1||+1||+5||-||Your First REAL set of Level 2 Spells. Aren't you happy? Boost that Dex Score!|
|5th||Wiz1/Arc3/Mystic Theurge1||+1||+2||+0||+6||Whatever you Like.||And there you have it.|