Best Assassin build using only Paizo books?

[Angel Tarragon]

I need to create an assassin for game, but I've never built one for Pathfinder before. I could use some advice...or maybe a link to stats to one that has already been made.

[Movin]

Thats a fairly broad term.
Pathfinder has all manners of killing people with stealth.
What kind of stealthy killer would you like first off?

[Rub-Eta]

First, you really need to define what about an assassin you want within this build.
Then you need to identify what aspects of the rules that will fulfill your goals and find a sustainable combination between the best options.

Ex:

If you want to be undetectable and sneaky: High Stealth (and Dex) and/or Invisibility/Vanish and/or Silence can help/achieve this.

Being able to travers and scale buildings and other obstacles with ease to get where you want: High Acrobatics (and Dex), high Climbing (and Str), ability to fly/cast Fly, cast Spider Climb, cast Jump. Other options could be Dimension Door and other teleportation spells.

Getting in where you want: High Disable Device or able to cast Open/Close and/or Knock (so that you don't have to knock on the front door when you get there).

Being able to "assassinate"/kill one enemy very quickely: This is probably the hardest one and at the same time the easiest one. Good old damage optimization. However, a lot of that is hard doing the assassin way. A lot of concepts of an assassin means that they'd use Coup de Grace and not straight up combat. The hard part is getting to that position (use stealth?).

Poisons? It's a bit suboptimal to do poison builds in Pathfinder. A lot of them rely on WBL and external items (the actual poisons) to support their mechanics.

From what is seems, a Ninja, Bard or a Wizard (or Sorcerer) seems to be the best class.

If you're the DM, this is a lot easier.
If you're the player, remember that this is a very niche concept and hard to fulfill in many games, as assassins operates in a different way than most killer-hobo partys. If your entire party consists of assassins (and you're playing in an assassin game), take a look at what the other players already have and what they don't have: they won't need two people stabbing the knif or picking the lock.

[CWheezy]

Wizard is the best assassin.

[MageHunter]

I would try investigator. That with the assassin prestige class. The skills and abilities mesh. Assassin just walks up, assassinates, and walks away. A drow that uses SLA's to blind foes would be fun.

[wraithstrike]

That Assassin PrC sucks at it's job. It has to hide, and once detected it is almost impossible to use its ability again during the fight. It has to hit, and it death feature's DC is based off a tertiary stat.

I would go with a wizard/sorc/arcanist.

If you want a traditional melee assassin then it might depend on what levels you will go to or what level the NPC will be if you are the GM.

[Covent]

I found alchemist and some of its archetypes specifically vivisectionist to be a good fit for an assassin. You can get stealth poison and decent short ranged attacks.

[MrKurtz]

Inquisitor "Sanctified Slayer" 12, Horizon Walker (Urban or Mountain/Astral Dominance) 6, Monk 2. Use Dimensional Chain. 3d6 Sneak Attack "Always Flanking" + 4d6 Bane + attack damage. Stalwart and Evasion.

[MrKurtz]

Witch 2 w/ Slumber Hex
Heavens Oracle 2

[I3igAl]

Antipaladin could do the job as well. Gets Seneak and invisibility, can take the target out with afflictions and is a rather strong oponent on his own.

On Spell I would use as a Alchemist(Vivisectionist)/Full Caster Assasin is Skinsend.

Silence is also a great tool here.

Aracane Tricksters could make for interesting Assasins.

[Slithery D]

The Velvet Blade archetype for the Slayer provides options for talking your way into position to stab someone with sneak attack bonus damage (more than your usual) in a social situation.

[Atarlost]

Probably druid. Nobody pays attention to common diminutive animals. Except in some cases to set traps that only work because rodents aren't very bright. Or they get a cat.

Poison isn't as bad as natural poisons and natural poisons produced by wildshaped druids have DCs in accordance with the druid's hit dice and con modifier. Contagion is also useful if you can re-apply it.

A level 8 druid can turn into a diminutive mouse, sneak into a bedroom, hide under the bed, and then drop wildshape and coup de grace the target with a scythe when he falls asleep. Or turn into a dire tiger and pounce and grapple him. Or turn into a tiny poisonous snake and hold a charge of pernicious poison and poison him with actual useful DC and duration. Then follow up with spit poison and maybe spam nauseating dart to keep him from fighting back. Then the druid uses his third wildshape to turn into an escape form, probably either a bird or bat to fly away or back into a mouse to sneak out.

Someone prone to hunting, as nobles often are, can be ambushed with stench of prey as an opener, leaving his companions too busy preventing him from being ripped apart by his own hunting dogs to prevent him from being pounced. Use charm animal to gather some minions to keep him from escaping and maybe dominate his horse.

As you advance wonderful things like greater contagion and rest eternal to make victims stay dead.

[BadBird]

What kind of level of character are we talking about here? It makes a huge difference. If we're talking about high enough levels that things like Dimensional Dervish are in play... For that matter, can the character be built as if retraining is fine?

[Zwordsman]

Toxicant Alchemist can sure do a lot of similiar stuff.
Either bomb or sneak attack versions of them both have benefits depending on whch kind you wan tto be.

[BackHandOfFate]

Serpent Shaman archetype for druid is pretty good at all the things an Assassin has to do. You can wildshape into diminutive snake forms as early as level 6. You get access to the TRICKERY DOMAIN!

There's more to it. But Altarlost already pretty much covered the basics of how awesome vanilla druid is at this job.

[Dave Justus]

If you just want someone that can take out a single person fairly reliably, the Red Mantis Assassin prestige class is actually pretty dangerous.

Prayer attack doesn't work well for fighting a group, but against a single victim it can be pretty deadly.