The equipment detailed here offers sneaky combat options for thieves, which any character with any real decency and sense of honor would usually eschew. Since by definition some of these items subvert normal combat options, the DM should feel free to modify and/or restrict the availability of items he feels unsuited to his campaign. the concealed weapons listed, at the least, should definitely be made available to thieves who are members of Assassins' Guilds.
Blinding Powder[]
This is a general term for any powder which is highly abrasive, irritating to the eyes, and disabling to the victim as a result. Powdered stone, pepper, dust soaked in onion juice, and strong ammonium salts—blinding powder can be made from many ingredients.
Blinding powder is only useful if it is thrown right into the eyes of a victim. This counts as a called shot (Dungeon Master's Guide, p. 58) with an additional (doubled) penalty, for a total of -8 on the attack roll. the Dexterity bonus of the person throwing the powder applies to the attack roll. Further, the base AC of the target ignores any armor or shield used, save for the use of a helmet or helm; magical protection such as bracers of defense or a ring of protection protect the target, as does Dexterity (unless the attack has an element of surprise).
If blinding powder strikes a victim the effects are the same as those of the stinking cloud spell save that they last for 2d4+2 rounds and no saving throw is allowed. If the victim can wash his eyes with plenty of water, the effect will only last for one round after the eyes are washed. Although blinding powder can contain some unpleasant ingredients, it has no permanently damaging effects on the eyes.
Death Knife[]
This sinister instrument can appear to be a bladeless knife, but it is more often disguised as something more innocent such as a case for a comb or spectacles or quill pen, a tool of some sort, etc. The disguise will not fool any close inspection, however. The blade of the knife is within a barrel inside the handle and is spring-loaded. The knife is triggered by pressing a catch on the handle; the blade shoots forward with considerable force. The weapon does the same damage as a normal dagger, although one point of damage is added for a first strike when the blade is triggered.
The obvious advantage of the death knife is its capacity for surprise. Since it doesn't look like a weapon until the blade is sprung, a victim can be taken totally off guard by its use. If the target does not realize a blow is coming and the thief manages to get the weapon close to the body of the victim so that a lunge can be made with it, any strike is treated as a backstab, with standard hit and damage bonuses, given the surprise element. A backstab is not always literally a stab in the back!
An envenomed death knife in the hands of a skilled assassin is an extremely dangerous weapon, and the DM may wish to rule that since the blade has to be concealed for some time before a strike there is a 25% (or higher) chance that the poison will have dripped from the blade before the assassin strikes with it.
Folding Bow[]
Bows are very useful for thieves, but are very hard to conceal because of their size and shape. A folding bow solves this problem, dividing neatly in half when unstrung, making it a much more suitable size and allowing concealment—for example, in a thigh sheath. Only short bows have folding-bow equivalents.
The joint in the middle of the bow weakens it, however, reducing the effective ranges to S 4, M 8, L 13, and also making it -1 on damage rolls (but any hit causes at least one point of damage).
Pin Ring[]
This simple weapon is a ring with a flip-up lid, below which is a needle capable of delivering a dose of poison (or knock-out drug, etc.) to the target. The most primitive version of this will have the pin simply sitting in a small reservoir of liquid drug or toxin. Since administration of the poison/drug is rather haphazard here, the victim receives a bonus of +2 to any saving throw against its effects. Subtler and more refined designs have a needle capable of drawing up liquid from a reservoir, so that only a normal saving throw (or even one with a -2 penalty) applies. The DM should decide which to allow in the campaign (both can exist at the same time, of course).
An attack with a pin ring is a called shot (with a -4 penalty to the attack roll) because it must strike exposed flesh—the pin will not administer poison through any significant thickness of clothing. A strike to the neck is the time-honored way of making sure the toxin gets into the bloodstream quickly. The DM may rule in unusual cases that no called shot is needed (e.g., the thief surprises a victim in his bath) or that the pin ring cannot be effective at all (e.g., the victim is clad from head to toe in field plate).
Sword Stick[]
This is simply a long, slender, rapier-like blade concealed within what appears to be a simple walking stick or cane. The long and thin blade requires a weapon proficiency slot to be used most effectively. Swashbucklers are particularly fond of this weapon. Damage done by the blade is as per a short sword. It takes one round to draw the blade from the sword stick and ready it for use. The main use of the weapon, obviously, is the possibility of smuggling it into places where weapons are not permitted.
It is highly doubtful whether anything like a sword stick existed in medieval times, but this weapon definitely adds some style and dash to a campaign. Since it does less damage than most swords (and requires a weapon proficiency) the DM should consider allowing it in his game.
Wrist Sheath[]
This small leather sheath is made to hold a knife or dagger, and is strapped to the forearm (below the sleeve of a garment) so that the weapon can be flipped to the hand by an arm movement and the blade readied for action. A dexterous thief can work a blade into his hand by arm movements disguised in the context of changing posture while sitting in a chair, or similar, seemingly innocuous moves. Again, the obvious advantage is that of concealment.
Variants on this theme are drop sheaths, which are usually sewn into leather jackets or similar articles of clothing. Here, release of the dagger from the sheath can be triggered by mechanical means (pressing a jacket sleeve stud, etc.) or by muscular stimuli triggering pressure pads (tensing the biceps firmly against the fist of the other arm, etc.).