Potentially having a game in the near future where we are using material from Heroes of the Jade Oath. It will be a one shot, taking place at level 13. I saw the flying guillotine and thought, hmmm? How to build around that!?
Class: 1-hand
Category: Thrown
Fighter Weapon Grouping: Thrown
Damage Type: S 1d8
Critical: 18-20/×4
Cost: 50 gp
Category: Weapon
Weight: 5 lbs
This 15-foot length of chain has what appears to be a chain-linked birdcage at the end. It is large enough to fit a Medium-sized humanoid head. Razor-sharp blades rim the bottom edge of the cage. They contract in a slicing motion when the wielder pulls the chain. This is a vicious ambush weapon attackers usually slide over a target’s head from above. The weapon does no damage until the blades are triggered. Using this weapon requires a standard attack action to hit a target and then a move-equivalent action to trigger the blades. Although the chain is kept in hand, treat it as a projectile weapon with a maximum range of 15 feet and no range penalties.
Dealing no damage until you use a move action to trigger the blades could be a problem. We would be limiting ourselves to a standard action to attack with.
I'm thinking going for two weapon fighting (not improved) route, but only the one feat. Then picking up Weapon Trick (two weapons) and using the Dual Strike trick. Getting a third arm (or extra set of hand) to trigger the second set of blades (like a familiar or vestigial arm) wouldn't be out of the question. Vital strike feat(s) should still work, though the effect is delayed until just after the attack.
What's the damage dice of the weapon? That makes a big difference when determining if it will be worthwhile to benefit via Vital Strike, because it may otherwise be a waste of feats if all you're increasing is a D6 of damage.
The Two Weapon trick won't help since you have to spend two move actions, one for each weapon that you're hitting with. Unless you have an ability that lets you take two Move Actions simultaneously, this is actually just a trap.
Additional limbs won't help you either, as they don't grant you additional actions, just additional ways to carry out the actions you already have.
For the record though, the only reason that weapon isn't OP is because it's murdered by its horrible action economy and locked behind the Exotic Weapons barrier. It's otherwise extremely devastating pre-6 if you can get the proficiency for it for free.
I updated the original post with missing information (damage dice).
I am aware that I need two move-equivalent actions to trigger the damage on the weapon. Since it is effectively "pulling" on the chain afterwards, the ability to withdraw an item or another weapon "quicker", like QuickDraw, might be convincing enough to a DM. Otherwise, having a familiar spend an action to give the other chain a "yank" should suffice.
Barring the hurdles, what would you do to make it effective to use this weapon, even if you were limited to a single attack and move action to use it at all? Bear in mind that using enlarge person is likely to occur, so I can effectively hit bigger enemies.
You can try to convince the GM that it could work, but I don't know your GM, so I can't give advice on that front. I would instead suggest to hope for the best (that he allows it to work), but expect the worst (that he demands an actual move-equivalent action to do so), and as such, not plan around it.
To that end, I have an alternate idea.
Go Warpriest, preferably Arsenal Chaplain archetype for Weapon Training, granting bonuses to attack and damage (as well as Advanced Weapon Training goodies later down the road) to shore up your 3/4 BAB, and purchase Gloves of Dueling for more to-hit and damage (and Advanced Weapon Training scaling).
Pick up the Ricochet Toss feat or the Returning weapon property so you can attack each round (you have to throw it, doesn't mean it won't come back to you automatically just because you have a chain on it).
The damage dice of the weapon will scale with your class level, improving to 1D10 for base dice. From there, you can use Enlarge to make it 2D8, and Lead Blades for 3D8 (Impact property, per RAW, wouldn't increase it since it applies to the weapon's base damage, and not the actual damage of what you're wielding in the case of Lead Blades).
Snatch the Vital Strike feat chains (starting at 13th, you can possess Improved Vital Strike), and you're doing 9D8+Strength+Weapon Training+Enhancement Bonus+Power Attack/Deadly Aim, all on a single hit, at your highest BAB, per round.
The downside is that you can't Enlarge and Lead Blades by yourself, though if you can convince your GM to let you apply Quick Draw to the weapon's mechanics, I imagine you can convince your GM to let you purchase items that let you use these spells 3+ times per day.