The two core abilities "Combined Spells" and "Spell Synthesis" stay pretty much unchanged. Due to the high overlap between arcane casters I added additional abilities to make the prestige class more interesting.
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Requirements:
Able to spontaneously cast 2nd level arcane spells
Able to cast prepared, arcane spells of 2nd level.
Knowledge Arcana (3 ranks)
Skills:
Knowledge(Arcana), Spellcraft
Other basics:
Skillpoints, BAB and Saves are identical to the Mystic Theurge.
Spells:
Each level increases spell casting in one spontaneous casting class and one prepared casting class.
Specials:
Combined spells: Works analogous to the Mystic Theurge ability with the same name.
Redundancy: If you have (or had if you cast it already) a spell prepared which is also among your spells known, you can modify one or more aspects of this spell.
You have to use a swift action to apply the modification(s). Spells you have transferred to the other class via the "Combined Spells" ability do not count for Redundancy.
At 2nd level you can apply 1 modification to a spell. Every two levels after you can add an additional modification (up to a maximum of 4 at level 8) to the spell. You cannot select the same modification more than once. Note that some choices count as several modifications!
These modifications count as one mod.
- Increase the caster level of the spell by 1.
- Increase the DC of the spell by 1.
- Increase the duration of the spell, as if your caster level was 2 higher.
- Increase the spell's maximum damage dice by 2.
- Increase the range of the spell as if your caster level was 3 higher.
- Gain a +2 bonus on caster level checks to overcome spell resistance.
These modifications count as two mod.
- If the spell effects more than 1 target, it can effect 1 additional target.
- If the spell creates more than 1 missile, ray or projectile it can create an additional missile, ray or projectile.
This modification counts as three mod.
- If a spell can only effect a certain creature type (such as Hold Person) you can attempt to make it apply to a different creature type. First you make an appropriate Knowledge check (move action, DC = 10 + CR) to identify the creature. Then you cast the spell spending a swift action to modify it as normal. Once you have spent the move action to identify you have to begin casting the spell in the next round at the latest. Should your knowledge check fail the spell is still cast and has no effect (you don't know if the spell has an effect or not until you have cast it).
This modification counts as four mod.
- If you cast a spell with a range of personal you can have it effect another creature than yourself with it. A minimal amount of concentration is necessary each round (free action) to keep the spell active on your target which means you must stay within close range of the target or the spell dissipates.
You cannot have more than 1 personal spell active on another creature at the same time.