
ohako |
Here goes nothing
Underhanded* (Ex): A rogue with this talent gains a +4 circumstance bonus on all Sleight of Hand checks made to conceal a weapon. Furthermore, if she makes a sneak attack during the surprise round using a concealed weapon that her opponent didn't know about, she does not have to roll sneak attack damage, and the sneak attack deals maximum damage. A rogue can only use the underhanded talent a number of times per day equal to her Charisma modifier (minimum 0).
The key line here is 'concealed weapon that her opponent didn't know about'. I've always thought this meant that the rogue can't initiate the surprise round by drawing a concealed weapon (as a standard action), or brandishing an obvious natural weapon, or sniping. Instead, the rogue has to 'unconceal' a hidden weapon as a free action somehow (spring-loaded wrist sheath or a heavy wrist launcher), and then do the deed.
Conceal Spell: When you cast a spell or use a spell-like ability, you can attempt to conceal verbal and somatic components among other speech and gestures, and to conceal the manifestation of casting the spell, so others don't realize you're casting a spell or using a spell-like ability until it is too late. The attempt to hide the spell slows your casting slightly, such that spells that normally take a standard action to cast now take a full-round action, and spells that normally take longer than a standard action take twice as long. (Swift action spells still take a swift action.) To discover your ruse, a creature must succeed at a Perception, Sense Motive, or Spellcraft check (the creature receives an automatic check with whichever of those skills has the highest bonus) against a DC equal to 15 + your number of ranks in Bluff or Disguise (whichever is higher) + your Charisma modifier; the creature gains a bonus on its check equal to the level of the spell or spell-like ability you are concealing.
If your spell has a somatic component, any creature that can see you receives a Perception or Spellcraft check (whichever has the highest bonus) against a DC equal to 15 + your number of ranks in Sleight of Hand + your Dexterity modifier; the creature gains a bonus on its check equal to the level of the spell or spell-like ability you are concealing.
Since you are concealing the spell's manifestation through other actions, others observing you realize you're doing something, even if they don't realize you're casting a spell. If there is a verbal component, they still hear your loud, clear voice but don't notice the spell woven within.
If an opponent fails its check, your casting also does not provoke attacks of opportunity, and an opponent that fails its check can't use readied actions that depend on realizing that you're casting a spell or using a spell-like ability, or readied actions such as counterspelling that require identifying the spell you're casting. Spells such as fireball that create an additional obvious effect (aside from the manifestation of casting that all spells and spell-like abilities share) still create that effect, though it might not be obvious who cast the spell unless it emanates from you.
If a character interacts with you long enough to attempt a Sense Motive check without realizing you have been casting spells, that character can use Sense Motive to gain a hunch that you're behaving unusually.
So. Let's say a Cha 16 rogue has the minor magic rogue talent, selecting acid splash. And the rogue also has the underhanded talent, and the Conceal Spell feat.
1) Underhanded grants a +4 on the check to conceal a weapon. I know it's not a check, but would underhanded grant +4 to the DC to notice the somatic components of a concealed weapon-like spell?
2) If this rogue successfully conceals a casting of acid splash, does this satisfy underhanded's condition of 'a concealed weapon the opponent didn't know about'? In other words, is it 'too late'?
3) Not a rules question: good gravy is underhanded circumscribed. A talent from Ultimate Combat only works with something from Ultimate Intrigue or the Adventurers' Armory? Plus, a rogue with a low Charisma can take the talent and have it literally do nothing. Is there any other ability where 'minimum 0' is a thing? Plus, only pretty rogues get to be underhanded? What does Charisma even have to do with it?

Trekkie90909 |
1) No, it's not a Sleight of Hand check. Worth asking your GM anyways, but this is the rules forum, and that's the rules answer.
2) Yes, so long as there's no reason for the enemy to know that you have that ability. A traveling companion, for example, might know of the ability, and the underhanded talent would not apply.
3) Best to ask this in a different thread, on a different forum; I'd suggest homebrew/suggestions/houserules, although there are a couple others which are broad enough to encompass the topic (general discussion, various AMA threads in off-topic, and product feedback come to mind). The less-than-helpful rules answer is "because that's what it says."

ohako |
Hmm, not sure I buy the 'you're protected if you know it's coming' defense. A half-orc with Surprise Follow-Through will still 'surprise' foes when using Cleave, even if the surprise is spoilered. In this case, making your opponent's head explode with acid splash only works during the surprise round, so that's a limiting factor.

Trekkie90909 |
A rogue with this talent gains a +4 circumstance bonus on all Sleight of Hand checks made to conceal a weapon. Furthermore, if she makes a sneak attack during the surprise round using a concealed weapon that her opponent didn't know about, she does not have to roll sneak attack damage, and the sneak attack deals maximum damage. A rogue can only use the underhanded talent a number of times per day equal to her Charisma modifier (minimum 0).
See bolded text.