[RPG] How to cast a spell that’s not on the spell list without spending points in Use Magic Device

Based on the alternative class features thread, here are your options:

Rogue

• Antiquarian – +Wis to Appraise for divine items, can attempt to identify divine items
• Changeling Rogue – 10+Int skills/level, one Knowledge skill of choice as class skill, gain Social Intuition (several special features with social skills)
• Drow Rogue – Poison Use
• Mimic – Disguise self

Scout (none)

So only one that you missed, but it’s a really good one. Anyway, rogue/scout seems like a kind of poor multiclass to me; they overlap on a lot of things and their primary differences don’t synergize very well (rogue wants to flank, scout wants to move).

With the build I'm going for the Drow Rogue looks the most viable but really poison use appears to be more trouble than it's worth (especially with the cost of decent poisons...)

Poison Use is almost useless; if you want to specialize in poison, you really want the Master of Poisons feat from Drow of the Underdark, which gives you Poison Use and the ability to poison a weapon as a Swift action.

That said, poisons can be worthwhile, and better you can make decent use of poisons without investing heavily in them. Having Poison Use rather than Master of Poisons is mediocre, but Craft (poisonmaking) can generate substantial savings on poisons (prices as low as ⅙ the base cost). Tossing a few points in Craft (poisonmaking), carefully selecting cost-effective poisons, and having Poison Use can give you a fairly potent low-level option.

For more about making the most of poison, check out Arsenic and Old Lace.

RAW: Ambiguous

The rules are not clear on what, exactly, constitutes an “arcane spellcasting class” or a “divine spellcasting class,” probably because initially it was obvious. By default, assassins, bards, sorcerers, and wizards were the arcane spellcasting classes, blackguards, clerics, druids, and paladins were the divine spellcasting classes. There was no ambiguity: the former are the classes that cast arcane spells, and the latter are the classes that cast divine spells. Easy.

Then they printed things like Alternate Source Spell, Rainbow Servant, Sha’ir, and Southern Magician, which introduced ambiguity that hadn’t existed before. In these cases, you have spell slots from one class being used for either arcane or divine spells.

Does this new feature suddenly make the class into an “arcane spellcasting class” or “divine spellcasting class” where it wasn’t before? There hadn’t ever been a strict definition before, and they didn’t print one at this point, either. Some of these effects seem to try to include wording that prevents this kind of thing, but much of those rules are also unclear. For instance, consider this from Southern Magician: “The actual source of the spell's power doesn't change,” which Customer Service interpreted as preventing entry to mystic theurge. But it doesn’t really say that, does it? It says something about power source, which is unclear.

Unfortunately, there’s no direct, rules-as-written, “as it says on page xyz of Complete Shenanigans” kind of answer to this question.

Recommendation: Never

RAW is ambiguous, but what’s going to work well in-game is not: never, under any circumstances, should one be allowed to advance wizard spellcasting faster than the wizard does. That should never, ever happen in any game, and if you’re going to allow it you might as well allow Pun-pun.

Allowing these sorts of tricks to qualify for mystic theurge, and other prestige classes and feats that require one type of spellcasting or the other, is pretty clearly legal, RAW, and also usually far less troublesome. The only exception I’d be likely to make is the dweormerkeeper from Complete Divine’s web enhancement, but then I’d probably just ban that class outright.

Even allowing a divine-only prestige class to progress wizard spellcasting is almost-always not a problem. It’s the double-progression that should never, ever happen.