Alright, so, I have an idea for a feat to introduce into my tabletop D&D game using 3.5 rules, but I would like some feedback on it from anyone who had a pretty good knowledge of 3.5, or anyone who has suggestions on how to tweak it. I already reasoned a lot of this feat out with a buddy, so it shouldn't be too sloppy.
Feat: Concealed Strike
Prerequisites 8 (or 11?) ranks in Sleight of Hand
Benefit: By taking a -4 penalty on your sleight of hand check, you may conceal a weapon in such a way that you may use a standard action to attack with it. Using a full round attack negates any benefit after the first attack. Anyone who fails to notice the concealed weapon (via opposed spot check) is also unable to see you make your attack with this weapon. Any target attacked with a weapon so concealed loses his Dexterity modifier to AC, but gains a circumstance bonus to spot your weapon on his next combat round. This bonus is +5 for ranged weapons, and +10 for melee weapons, this bonus is cumulative for each round an attack is made against this target within 1 minute of the last attack. A succesful spot check by the target prevents that weapon from denying him his dexterity bonus to AC until it is concealed again. If you make another attack with your concealed weapon within 1 minute of the last, every creature with a line of site gets a cumulative +2 circumstance bonus to their spot check.
Okay, so, the idea behind this feat is to allow for a stealthy character (particularly Assassins) to be able to harrass some people in public without arousing too much suspicion, to be able to strike, and blend seamlessly back into the crowd, and to give rogues another way to utilize their sneak attack.
Using the rules as-is, the only way to do something similar is to attack, then take the -20 penalty to Sleight of Hand in order to conceal a weapon as a free action, and to hope you have a kind DM.