Pathfinder Alchemists were introduced in the Advanced Player's Guide. They are basically a mad scientist character class. They cackle, they drink mutagen and turn into the Hulk, they make construct-soldiers out of dead bodies, they cast spells by chugging potions, you get the idea. Alchemists are solidly tier 3, capable of doing a few things very good (damage, skill monkey) and still contributing when those things aren't useful through their wide variety of extracts. One pair of discoveries gives Alchemists access to the Simulacrum spell, which is broken enough on its own (Making a clone of a high level beat stick that follows your commands is the least creative way to break it.) they become tier 1 if taken.
Mechanically, Alchemists get three tricks. The first are alchemical bombs, which are splash weapons that they can prepare a certain number of per day. The second are infusions, which are bottles of magic that are prepared like Wizard spells but drunk like potions. The third is mutagen, which is basically Mr. Hyde juice; mechanically, it buffs one of your physical stats at the expense of your mental stat, and too much stat damage will cause sudden reversion.
Alchemists are a lot of fun, since they get Throw Anything as a power and have lots of unique bombs they can make, and actually make "incredible discoveries!" as they level up, ranging from growing new limbs and tumors that fall off and act as familiars to learning how to cheat and bottle spells they shouldn't theoretically have. There's nothing else in the game quite like them, and it makes them unique and interesting. Unfortunately, all those powers aren't terribly focused, which is a downer. If you want to build a decent alchemist, pick one or two of their mechanics and leave the third by the wayside. Oh, and everyone will hate you if you don't take the discovery which lets other people use your infusions, which you should do anyway, because what else are you going to do with that enlarge person potion? Wade into melee? My 30+ AC, 3 Nat attacks a round, and +12 to Hit suggest that that is a good idea as long as the mutagen holds.
Also, they're very selfish casters that need to take a discovery just to let other people imbibe their spell-potions (though this does let them use Personal range spells on others and cast using the actions of other party members, which is nice), and without cantrips they can only identify potions without spending spell slots. As a result, they aren't the best solo-casters in a party full of melee beatsticks.
If you want a hilariously awesome class that does things you haven't necessarily seen before in the d20 system, pick this guy. If you want something a little more geared towards optimized mechanical play? I'm sure they'll have another overpowered wizard prestige class/archetype/pile of new spells ready for you in the next splatbook, you damn munchkin-robot.
Due to their popularity, they were included in the video game Kingmaker and the core book of the second edition of Pathfinder.
|The Classes of Pathfinder|
|Core Classes:|| Barbarian - Bard - Cleric - Druid - Fighter - Monk |
Paladin - Ranger - Rogue - Sorcerer - Wizard
| Alchemist - Antipaladin - Cavalier |
Inquisitor - Oracle - Summoner - Witch
| Arcanist - Bloodrager - Brawler - Hunter - Investigator |
Shaman - Skald - Slayer - Swashbuckler - Warpriest
| Kineticist - Medium - Mesmerist |
Occultist - Psychic - Spiritualist
|Ultimate X:||Gunslinger - Magus - Ninja - Samurai - Shifter - Vigilante|