If you are a serious sneak attacker, the best magic item in the core books is the Ring of Blinking. While you are blinking, every attack you make is a sneak attack. No more trying to surprise flat-footed foes. No more figuring out who you are flanking and who you are not. No more feinting or sniping. It is simple: every attack you make is a sneak attack.
(Well, yes, you can do the same thing without the Ring. The mage sneak attacker (such as an Arcane Trickster) can cast his own Blinks and Greater Invisibilities. With plenty of Use Magic Device Ranks, you can use scrolls and wands of those spells. But the idea is to achieve that state of perfection in which all your attacks are sneak attacks.)
Once you are sitting in that tactical catbird seat, it naturally behooves you to make as many attacks as possible. Thatís why a two-weapon fighting strategy is very attractive. So far, though, this screed is pretty redundant. Letís get to the second course.
One of the most impressive ways to get lots of attacks is with the Whirlwind Attack feat. With it, you can attack every opponent within reach once per round at your full BAB. To get the most out of ďwithin reach,Ē you want to use a reach weapon, like a spiked chain, that can hit foes near and far up to ten feet away. If you are a mage sneak attacker, then Enlarge Person is your friend, since your Enlarged reach with that spiked chain zooms to 20 feet.
The problem is, Whirlwind Attack takes a lot of devotion. Required feats are Combat Expertise, Dodge, Mobility, and Spring Attack. For a human rogue or rogue/mage, that means waiting until 9th level; for a non-human, such as a liontaur, even higher. Plus, the required feats are not really the ones you might have picked yourself, if they were not required. So you may want to consider the poor-manís Whirlwind Attack, Combat Reflexes.
With a 10- (or 20-) foot reach, foes moving in combat around and toward you are bound to provoke attacks of opportunity (AoOs). With a high dexterity (you DO have a high dex, right, oh you sneak attacker?), that translates into four or five or more AoOs a round. If an enemy both moves and casts while in your reach, you can make two attacks on that foe -- better than Whirlwind Attack. AND you get your normal attacks on your turn. All for the low low cost of just a single feat.
Which finally gets us to the whole point of this screed -- weapons. Whatís the best weapon for this kind of a strategy? To maximize your attacks of opportunity when it is the enemiesí turn, you have to have a reach weapon. To maximize your sneak attacks on your own turn, you want to fight two-handed.
You could contort your way around this dilemma with two gloves of storing. At the start of your turn, store your spiked chain and retrieve your staff or other double weapon. At the end of your turn (after making two-handed attacks), store the staff and retrieve the spiked chain, so that you can use it to make AoOs when others provoke them. But this is not only extremely kludgey and pricey (those gloves are expensive!), but it prevents you from wearing Gloves of Dexterity. And if you are trying to leverage your high dex with weapon finesse, that works fine with the spiked chain, but not so well with a double weapon.
Far far better would be to weild a one-handed reach weapon, freeing the othe hand for an off-hand attack. The problem is, there are not many one-handed reach weapons in the game. Letís look at the two most obvious. The whip is a one-handed reach weapon, but it does not threaten any squares, making it useless (you have to threaten squares in order to make AoOs). The lance is one-handed if you are mounted. That is tough on those needing horses and ponies as mounts, since it is hard to get them down slimey dungeon stairs. If you are a halfling or gnome, using a lance while riding on dog-back is theoretically possible, but a realism-focused DM might balk at the way you whip that lance around in battle. Besides, a more ideal solution would include a one-handed reach weapon that works with weapon finesse.
At this point, the resurceful PC might be thinking about making their own one-handed weapon-finessible reach weapon -- maybe a barbed whip with a ten-foot reach and the ability to threaten squares. But donít go there yet, innovator! Monte Cook did you one better when he wrote the Asian Flavor section of the Dungeon Masters Guide.
Students, please open your texts now to page 144, and also study the table on page 145. Jimmy, would you please read aloud the section on the Kusari-gama?
Kusari-Gama: This small sickle is attached to a length of chain. A kusari-gama is an exotic weapon that has reach. It can strike opponents 10 feet away. In addition, unlike other weapons with reach, it can be used against an adjacent foe. It can be used in all respects like a spiked chain (see page 115 of the Player's Handbook) for trip attacks, disarming other foes, and using its weilder's Dexterity modifier instead of her Strength modifier in attack rolls.
Very good, Jimmy. And Joanie, what can you tell us from the table?
The Kusari-gama is an exotic light melee weapon. It costs 10 gp. It inflicts 1d6 base damage when used by a medium-size user and crits for x2 on a 20. It weighs 3 pounds. And it is a reach weapon that does slashing damage.
There you have it. A one-handed spiked chain. Since it is a light weapon, you can even use one in each hand at only a -2 to hit (with Two-Weapon Fighting). That makes feats like Weapon Focus (Kusari-gama) much more attractive. For the sneak attacking combat reflexologist, there is no sweeter weapon in all the core books. And to think you had never even heard of it!