Into every generation, a slayer is born. The slayer is a hunter, a stalker, and a killer, with enough power to fight fairly and win, but the inclination to fight unfairly and win by an even wider margin. The slayer combines the stalking and combat styles of the rogue and the ranger with none of the ranger's nature focus. Basically, the slayer is Ezio from the Assassin's Creed series, the quintessential assassin and the last person you want to see leaping out at you from the shadows.
The slayer is a full BAB class with a slower sneak attack progression than the rogue, talents at even levels, and its own prime feature, favored target (which is now called studied target). Studied target is the slayer's spin on favored enemy. Instead of hating a particular type of creature, the slayer studies any target he wants (hey, no wonder it's called studied target!), gaining bonuses against that target until he switches targets. Since this bonus also applies to Bluff, Knowledge, Perception, Sense Motive, and Survival (and later Disguise, Intimidate, and Stealth), clever slayers can also gain a substantial boon from this feature in a variety of non-combat situations as well by studying NPCs during social encounters too. Favored target has unlimited daily uses, and who knows—if the old lady suddenly starts attacking, then you're even ready to fight back right away!
In the original version, there were 16 choices for slayer talents with 8 additional advanced talents available at level 10. Playtesters had trouble finding enough talents that they wanted to take for their builds, so for the second playtest, this increased to 24 talents and 10 advanced talents, including the powerful combat style talent that could be taken three times, essentially granting the ranger's combat style feats to the slayer, and allowing the slayer the potential to amass a small army of feats at his disposal. Additionally, playtests had shown that the slayer's 4+Int bonus skill points were insufficient to pick up all the sorts of skills he needed to successfully slay, so he bumped up to 6+Int skill points.
The final version of the slayer as it appears in the Advanced Class Guide is quite similar to the second playtest version, so pull up your playtest document (or download it now) for an excellent preview of the class. The most exciting change is in the action economy of studied target—at low levels (before 7th when you can study as a swift action), melee slayers were finding the move action to study a target was really cramping their ambushes. So now, starting from level 1, if you hit and deal sneak attack damage, you can apply your studied target as an immediate action, and it even applies the favored target bonus to damage for that same attack. That way, you can ambush all you like and get right to the slaying!
The slayer screams out for archetypes that capture all the different facets of the iconic image of the slayer. The slayer archetypes in this book are really nice in that they give you what you're looking for with a relatively light touch, generally switching out a few of your talents for thematic abilities and losing very little else. The bounty hunter is your Boba Fett, bringing back criminals and debtors alive with combat maneuvers and an incapacitating death attack. The cleaner is the guy you send in to make sure those darned investigators don't figure out what happened, with a special ability to force any would-be detectives to beat the cleaner's Disguise or Stealth in order to find clues. The cutthroat is even more like Ezio, losing outdoorsy skills for city-based powers and skill bonuses that will help you leap off buildings instead of out of the shadows. The grave warden goes back to my intro quote with a kickass undead slayer, gaining an at-will self-only death ward at level 7 (it does cost 4 holy waters) and the ability to death attack an undead. But I'm sure you've been wondering "Mark, when are you going to get to that glowy purply shadow guy. He looks awesome!" That, my friends, is the stygian slayer, a killer imbued with the darkest shadows. He can cast invisibility, use wands and scrolls of a few thematic spells without a Use Magic Device Check, and turn into an inky black cloud that obscures vision. And that's just 5 of the 8 slayer archetypes in the final book! But wait—people have been asking for a thrown weapon ranger combat style for a while, right? Yeah, we have that too!
So you've got the rogue. You've got the ranger. Why should you be excited about the slayer class? Because those other classes serve a few masters when it comes to their design, but the slayer unashamedly serves only one—he wants to be the best at slaying, eliminating a chosen foe or foes. And he serves his master well. Even a fighter's offense can't keep up with the slayer, so if you prefer a style that emphasizes guile, stealth, and strong offense over defense, the slayer is the class for you.
As I'm typing this last paragraph, I've noticed that the slayer has some kind of a curved dagger to my throat, and he's made a few demands, so I want you to know, completely not under duress, that the slayer is my personal hero and is the best at all things. In fact, we're going to put out an entire book dedicated only to slayer options, and—aaaaaargh.
Editor's Note: After shooing the raptors away from the scene, we found this blog on a USB drive clutched in the hand of the remains of designer Mark Seifter. After a resurrection spell, he's fine now and back at work on Pathfinder Unchained, but he's still jumpy any time anyone mentions the slayer class. He defies anyone who claims that if he was dying, he wouldn't have bothered to have typed "Aaaaargh", he'd just say it.