Milly Tanner, Arcane Trickster (Unchained Rogue/Greensting Slayer Magus)

The folks at Iconic Design (darn ya Alex.. you're truly awesome at this) brought up some excellent tricks with the Dirty Tactics Toolkit that make up a good way to save a few caster levels. Specifically one feat, Accomplished Sneak Attacker, which gives an additional 1d6 to sneak attack.
Why is this important you ask? Because it's the difference between 1 and 3 levels of rogue. This way you get the 1 level you need to make certain skills class skills (cause anyone who wants to disable locks is going to want to be able to do it +3 skill better)
For me there are two important things in this build:
- Accomplished Sneak Attacker: Dirty Tactics Toolkit
- Sense Vitals: A spell that lets adds +1d6 sneak attack/3 levels (5d6 @15th cap) to any manufactured weapon you attack with. NASTY. Add in the reddish glowing eyes you have while it's in effect for the creepy factor.
Class Selection: Unchained Rogue and Greensting Slayer Magus. I like the UC rogue a lot and if you decide to do a few levels dip instead of taking Accomplished Sneak Attacker, it has some nice benefits to 2 more levels of UC.
Greensting Slayer Magus is another source of sneak attack damage. Granted its only +1d6 with a swift action in the levels you get out of it but it's another 1d6.
The whole plan is to give the magus a bit more utility than outright 'touch attack with weapon attack', rinse, and repeat. With sneak attack damage and even more courtesy of her arcane pool and/or sense vitals, sneak attack makes up for not using as many spells to keep up the damage. Assuming a point of arcane pool being spent, Sense Vitals and normal sneak attack dice are in play; she can do 9d6 sneak attack in a single attack or 8d6 per attack during a full round of sneak attacking (assuming flanking). Fun note: the pool point only covers a single attack, so you can swap out Greensting for another archetype or even a vanilla magus. Though it does provide that extra bit of umph till you can get Spellbinding (Sense Vitals) at 7th. You can hold off till 9th level when you get 2 spells for the arcana but I'm impatient.

If you're lucky.. I'll just stab you

1st Level
Here we are at 1st level. Right now Milly is just a simple rogue, with a bit more intelligence than most and a hint of something arcane in her heritage (Blood of Dragons trait). She's got a wide variety of choices in weapon selection, with 14 Str/Dex, among any. For this particular build I'll be working towards a bastard sword but with a little 'flexibility' in skill selection could have enough dance to pick out things like Dervish Dance (Which would allow him to use a scimitar and apply dex to damage, if you want to tweak out strength for more dex).

Milly Tanner
Female human (Varisian) rogue (unchained) 1 (Pathfinder Unchained 20)
N Medium humanoid (human)
Init +2; Senses low-light vision; Perception +4
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Defense
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AC 12, touch 12, flat-footed 10 (+2 Dex)
hp 10 (1d8+2)
Fort +2, Ref +4, Will +0
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Offense
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Speed 30 ft.
Special Attacks sneak attack (unchained) +1d6
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Statistics
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Str 14, Dex 14, Con 14, Int 16, Wis 10, Cha 10
Base Atk +0; CMB +2; CMD 14
Feats Combat Expertise, Fast Learner[ARG], Weapon Finesse
Traits blood of dragons, killer
Skills Acrobatics +6, Diplomacy +4, Disable Device +7, Disguise +4, Escape Artist +6, Knowledge (arcana) +4, Knowledge (local) +7, Linguistics +7, Perception +4, Sleight of Hand +6, Stealth +6, Use Magic Device +4
Languages Aquan, Common, Draconic, Kelish, Osiriani, Varisian
SQ trapfinding +1
Other Gear 150 gp
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Special Abilities
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Combat Expertise +/-1 Bonus to AC in exchange for an equal penalty to attack.
Low-Light Vision See twice as far as a human in dim light, distinguishing color and detail.
Sneak Attack (Unchained) +1d6 Attacks deal extra dam if flank foe or if foe is flat-footed.
Trapfinding +1 Gain a bonus to find or disable traps, including magical ones.

4th Level
Here we are at 4th level, with 3 levels of greensting magus for another die of sneak attack (if you use an arcana point). She can do sneak attack, spell combat and with close range to let her use spells like ray of enfeeblement to debuff her foes. Toss in vanish for 'instant' sneak attacks in the next round.

Milly Tanner
Female human (Varisian) magus (greensting slayer) 3/rogue (unchained) 1 (Pathfinder Player Companion: Bastards of Golarion, Pathfinder RPG Ultimate Magic 9, Pathfinder Unchained 20)
N Medium humanoid (human)
Init +2; Senses low-light vision; Perception +6
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Defense
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AC 12, touch 12, flat-footed 10 (+2 Dex)
hp 34 (4d8+11)
Fort +5, Ref +5, Will +3
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Offense
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Speed 30 ft.
Special Attacks magus arcana (close range[UM]), sneak attack (unchained) +1d6, spell combat, spellstrike
Magus (Greensting Slayer) Spells Prepared (CL 3rd; concentration +6)
   1st—chill touch (DC 14), ray of enfeeblement (DC 14), shocking grasp, vanish[APG] (DC 14)
   0 (at will)—acid splash, detect magic, mage hand, prestidigitation
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Statistics
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Str 14, Dex 14, Con 14, Int 17, Wis 10, Cha 10
Base Atk +2; CMB +4; CMD 16
Feats Combat Expertise, Exotic Weapon Proficiency (bastard sword), Fast Learner[ARG], Weapon Finesse
Traits blood of dragons, killer
Skills Acrobatics +9, Diplomacy +4, Disable Device +10, Disguise +4, Escape Artist +9, Knowledge (arcana) +10, Knowledge (local) +7, Linguistics +9, Perception +6, Spellcraft +8, Stealth +9, Use Magic Device +5
Languages Aquan, Auran, Common, Draconic, Ignan, Kelish, Osiriani, Varisian
SQ arcane pool, trapfinding +1
Other Gear 150 gp
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Special Abilities
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Arcane Pool (+1d6 sneak attack, 4/day) (Su) Expend Arcane Pool to add sneak attack dmg to next melee atk.
Close Range (Ex) Using spellstrike, deliver ranged touch spells as melee touch spells.
Combat Expertise +/-1 Bonus to AC in exchange for an equal penalty to attack.
Low-Light Vision See twice as far as a human in dim light, distinguishing color and detail.
Sneak Attack (Unchained) +1d6 Attacks deal extra dam if flank foe or if foe is flat-footed.
Spell Combat (Ex) Use a weapon with one hand at -2 and cast a spell with the other.
Spellstrike (Su) Deliver touch spells as part of a melee attack.
Trapfinding +1 Gain a bonus to find or disable traps, including magical ones.
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7th Level
Now we have Milly as a full on Arcane Trickster, thanks to putting in Accomplished Sneak Attacker @ 5th level for that 2nd die of sneak attack that we need for Arcane Trickster. Thanks to that we were able to hold off on 2 levels of rogue and get more spell levels earlier. So at 7th level, she can get Spellblending (1 spell: Sense Vitals) for even more sneak attack (3d6 from classes/feats +1d6 (greensting sneak attack) +2d6 (Sense Vitals)). It does require a MANUFACTURED weapon.

Milly Tanner
Female human (Varisian) arcane trickster 2/magus (greensting slayer) 4/rogue (unchained) 1 (Pathfinder Player Companion: Bastards of Golarion, Pathfinder RPG Ultimate Magic 9, Pathfinder Unchained 20)
N Medium humanoid (human)
Init +2; Senses low-light vision; Perception +10
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Defense
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AC 12, touch 12, flat-footed 10 (+2 Dex)
hp 54 (7 HD; 2d6+5d8+18)
Fort +7, Ref +6, Will +5
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Offense
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Speed 30 ft.
Melee bastard sword +6 (1d10+2/19-20 plus 1d6 sneak attack plus 1d6 sneak attack)
Special Attacks magus arcana (close range[UM], spell blending [1 spell][UM]), sneak attack (unchained) +1d6, sneak attack +2d6, spell combat, spell recall, spellstrike
Magus (Greensting Slayer) Spells Prepared (CL 6th; concentration +9)
   2nd—brow gasher[UC], darkness, mirror image, scorching ray
   1st—chill touch (DC 14), ray of enfeeblement (2, DC 14), shocking grasp, vanish[APG] (DC 14)
   0 (at will)—acid splash, detect magic, mage hand, prestidigitation, read magic
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Statistics
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Str 14, Dex 14, Con 14, Int 17, Wis 10, Cha 10
Base Atk +4; CMB +6; CMD 18
Feats Accomplished Sneak Attacker, Combat Expertise, Exotic Weapon Proficiency (bastard sword), Extra Arcana[UM], Fast Learner[ARG], Weapon Finesse
Traits blood of dragons, killer
Skills Acrobatics +12, Bluff +4, Climb +6, Diplomacy +4, Disable Device +13, Disguise +4, Escape Artist +9, Knowledge (arcana) +10, Knowledge (local) +8, Linguistics +13, Perception +10, Spellcraft +8, Stealth +12, Use Magic Device +8
Languages Aquan, Auran, Azlanti, Common, Draconic, Ignan, Kelish, Osiriani, Sylvan, Terran, Thassilonian, Varisian
SQ arcane pool, ranged legerdemain, trapfinding +1
Other Gear bastard sword, 115 gp
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Special Abilities
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Arcane Pool (+1d6 sneak attack, 5/day) (Su) Expend Arcane Pool to add sneak attack dmg to next melee atk.
Close Range (Ex) Using spellstrike, deliver ranged touch spells as melee touch spells.
Combat Expertise +/-2 Bonus to AC in exchange for an equal penalty to attack.
Low-Light Vision See twice as far as a human in dim light, distinguishing color and detail.
Ranged Legerdemain (Su) Can use Disable Device or Sleight of Hand from 30 ft away, but +5 DC.
Sneak Attack (Unchained) +1d6 Attacks deal extra dam if flank foe or if foe is flat-footed.
Sneak Attack +2d6 Attacks deal extra dam if flank foe or if foe is flat-footed.
Spell Combat (Ex) Use a weapon with one hand at -2 and cast a spell with the other.
Spell Recall (Su) Spend your Arcane Pool to recall spells you have already cast.
Spellstrike (Su) Deliver touch spells as part of a melee attack.
Trapfinding +1 Gain a bonus to find or disable traps, including magical ones.
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12th Level
Now at seeker level, Milly is a sneak attacking monster with skills in lock picking, magic device use, and so on. She can, when prepared, do HUGE sneak attack damage (5d6 (class)+ 1d6 (optional, Greensting Arcana) + 3d6 (Sense vitals)). Adding in fun things like Arden's spellsword (for storing a metamagic rod or wand/rod/staff of her choice) and spells like Greater Invisibility, Displacement, Blur, Mirror Image and such.
There are a variety of tactics you can use. Things like using invisibility/greater invisibility to summoning backup and such for the rest of the part. Add in two extra impromptu sneak attacks (courtesy of the feat x2) and you can do a bunch of sneak attack damage on demand. Tricky Spells means you can cast still/silent spells up to 4 times a day.

Milly Tanner
Female human (Varisian) arcane trickster 7/magus (greensting slayer) 4/rogue (unchained) 1 (Pathfinder Player Companion: Bastards of Golarion, Pathfinder RPG Ultimate Magic 9, Pathfinder Unchained 20)
N Medium humanoid (human)
Init +3; Senses low-light vision; Perception +15
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Defense
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AC 22, touch 15, flat-footed 19 (+7 armor, +2 deflection, +3 Dex)
hp 96 (12 HD; 7d6+5d8+40)
Fort +12, Ref +13, Will +11
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Offense
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Speed 30 ft.
Melee +2 dispelling keen adamantine bastard sword +11/+6 (1d10+5/17-20 plus 1d6 sneak attack plus 3d6 sneak attack)
Special Attacks magus arcana (close range[UM], spell blending [1 spell][UM]), sneak attack (unchained) +1d6, sneak attack +4d6, spell combat, spell recall, spellstrike
Magus (Greensting Slayer) Spells Prepared (CL 11th; concentration +17)
   4th—greater invisibility (3)
   3rd—aroden’s spellsword, displacement, fly, haste, keen edge
   2nd—mirror image (2), scorching ray, sense vitals (3)
   1st—ray of enfeeblement (3, DC 17), shocking grasp (2), vanish[APG] (2, DC 17)
   0 (at will)—acid splash, detect magic, mage hand, prestidigitation, read magic
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Statistics
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Str 16, Dex 16, Con 16, Int 23, Wis 10, Cha 10
Base Atk +6; CMB +9; CMD 24
Feats Accomplished Sneak Attacker, Combat Expertise, Exotic Weapon Proficiency (bastard sword), Extra Arcana[UM], Extra Impromptu Sneak Attack, Extra Impromptu Sneak Attack, Fast Learner[ARG], Weapon Finesse
Traits blood of dragons, killer
Skills Acrobatics +18, Bluff +4, Climb +7, Diplomacy +5, Disable Device +19, Disguise +4, Escape Artist +10, Knowledge (arcana) +21, Knowledge (local) +17, Knowledge (nature) +21, Knowledge (planes) +21, Linguistics +21, Perception +15, Spellcraft +16, Stealth +23, Use Magic Device +15
Languages Abyssal, Aquan, Auran, Azlanti, Common, Draconic, Elven, Hallit, Ignan, Kelish, Osiriani, Shadowtongue, Shoanti, Skald, Sylvan, Terran, Thassilonian, Tien, Undercommon, Varisian
SQ arcane pool, impromptu sneak attack, ranged legerdemain, trapfinding +1, tricky spells
Combat Gear extend metamagic rod (lesser); Other Gear +3 shadow mithral chain shirt, +2 dispelling keen adamantine bastard sword, belt of physical perfection +2, cloak of resistance +3, headband of aerial agility (int +4)[UE], ring of protection +2, 150 gp
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Special Abilities
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Arcane Pool (+1d6 sneak attack, 8/day) (Su) Expend Arcane Pool to add sneak attack dmg to next melee atk.
Close Range (Ex) Using spellstrike, deliver ranged touch spells as melee touch spells.
Combat Expertise +/-2 Bonus to AC in exchange for an equal penalty to attack.
Impromptu Sneak Attack (4/day) (Ex) You can declare any melee or ranged attack to be a sneak attack.
Low-Light Vision See twice as far as a human in dim light, distinguishing color and detail.
Ranged Legerdemain (Su) Can use Disable Device or Sleight of Hand from 30 ft away, but +5 DC.
Sneak Attack (Unchained) +1d6 Attacks deal extra dam if flank foe or if foe is flat-footed.
Sneak Attack +4d6 Attacks deal extra dam if flank foe or if foe is flat-footed.
Spell Combat (Ex) Use a weapon with one hand at -2 and cast a spell with the other.
Spell Recall (Su) Spend your Arcane Pool to recall spells you have already cast.
Spellstrike (Su) Deliver touch spells as part of a melee attack.
Trapfinding +1 Gain a bonus to find or disable traps, including magical ones.
Tricky Spells (4/day) (Su) You can cast a spell without verbal or somatic components.

Notes: There was a variety options here. Swap out greensting for a normal magus. Swap out EWP: Bastard sword for a scimitar and Dervish Dance. Wait till 9th level to get spell blending to get TWO spells rather one.

At A Glance: Pathfinder Unchained.

So, I sez.. 'betcha you won't pull that there chain...'

Pathfinder Unchained is what you get when you let the designers of the Pathfinder game brainstorm things out. Variant rules. Lots of them. New takes on the classes that have GMs tearing out their hair. Options and different takes on a myriad of things: Fractional Base Bonuses (saves/BAB and such), staggered advancement (variant version of multiclassing)

Classes: A new look at barbarian, monk, rogue and summoner.
 -Barbarian: Not too bad. More of a steamline and polish than re-balancing. Barbarian rage is now a simple +2 to melee attack/damage, thrown melee attacks and will saves, along with a penalty to AC, and temporary HP that goes first.. so you don't die from HP loss at the end of your rage. Rage powers are pretty much the same, with a few enhancements. You got a new category of rage powers: Stances. You can only use one stance power at a time, so there will be some switching.
-Monk: A tweak and polish to the monk. Full BAB and a tweak to flurry gives the monk teeth while throttling back the flurry mayhem. The big change (I've seen so far) is the ki powers; they are a very broad and selectable. Very wuxia in outlook. Style strike is added as well. One of the monk's flurry blows can be a style strike (with more as he levels) and have all sorts of fun effects.
-Rogue: One of my favorite classes, though I typically suck at it, but let's be honest there are oh-so-many options on how to do a 'trap monkey' now. You got to do a lot to make the rogue relevant when you got slayers, investigators, and all manner of archetypes and traits to get trapfinding in the mix. Most of what we get is polish, not much outright new. The new is finesse training, rogue's edge and debilitating injury. Finesse training is like what swashbuckler's get, an agile fighting style, but staggered. At 1st level, a rogue gets weapon finesse for free, at 3rd they get to add their dex (in stead of strength) to one finesse useable weapon with others being added later. Rogue's edge plays on the rogue's role as a skill monkey, adding on skill unlock powers to the skills they have. (More on that later) and finally debilitating strike which inflicts a a status condition when dealing sneak attack damage. Adding in tweaks and polish to rogue talents, I think they did a good job of pushing the rogue back into relevance.
-Summoner: If there was a class more hated by GMs than the summoner, I can't think of it. The summoner gets some tweaks and some justifiably needed re-balancing. Pretty much stays the same spellwise, with a few tweaks. Yeah, no more 2nd level haste spell kids. The big changes, naturally, are all around the eidolon. Each one now has a planar subtype as well as a body type. Each is aligned and a summoner can pick any 'adjacent' aligned type. Each gets perks and bonuses. Forms are tied to type: resistances, bonus to saving throws, dr and so on. All in all. I'm a hung jury on the summoner till I get to tweak my summoner and compare him to him as an unchained summoner.
-Factional base bonuses  & staggered advancement: Ways to advance/balance multiclass characters out. Meh to me.

Skills & Options: Background skills, consolidated skills, group skills, crafts/professions, skill unlocks and more on variant multiclassing. A variety of ways to streamline skill usage. Grouping skills by type, condesning them even further, and giving you a reason to specialize in a skill with Skill unlocks. You take a feat: Signature Skill, and go from there. Every five points you put in the skill comes an exceptional way you use it. I like that. Particularly for the rogues who now get one free @ 5th level. Lastly the multiclass alternates. (the stuff in classes is more phased advancement), this is more like the stuff in 4E multiclassing. Which I didn't like.
Gameplay: Gameplay elements like alignment, revising action economy, swapping out iterative attacks, tactics, wound levels and revised poison/disease. Tweaks and alternate methods of game play elements.
Magic: the big juice to me. You get rules for alternate spell casting as well as altering magic conditions (limited and wild magic) as well overclocking spells, spell fumbles, and esoteric material components and a few feats to juice things up. Then the last bit of the section is scaling items, and other approaches to magic items.
Monsters: More toys for the race/monster building crowd. Not my cup of tea but seems clear cut and good for making unique to your campaign folio of monster.

The crunch: Lots of it. particularly if you are a home gamer who wants to break with the usual mechanics.  It will be interesting to see what plays out in PFS and how much of this is followed up on in the splat books over time.