I'm fairly surprised this hasn't already been printed, since Alchemist is one of the few classes that can use poisons out of the box. I whipped this archetype up mostly because I was bored - as such it definitely needs balancing and may well be unplayable. I present it for your consideration nonetheless:
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New Class Features
Synthetic Venom: This ability replaces the Bomb class feature. A Poisoner can make a virulent toxin from chemicals commonly found in an alchemist's lab. This poison is prepared as a binary compound; it is inert until a final ingredient is added (as part of the action involved in applying the poison.) After the addition of the final ingredient, the poison remains potent for a number of rounds equal to the Poisoner's Int modifier, after which it is rendered inert.
When the poison is prepared, it acts as an Injury poison with an onset delay of 1 round. It inflicts 1d6 damage per round for a number of rounds equal to half your Poisoner class level. As a secondary effect, it deals 1 additional point of damage for a number of rounds equal to your Int modifier (so a level 1 Poisoner with 18 Int would have a poison that deals 1d6+1 damage in the first round, and 1 damage per round for 3 more rounds.)
Alternatively, the Poisoner may prepare his poison as an Ingested poison. It behaves identically as the above poison, except that it remains potent for a number of minutes equal to your Int modifier, has an onset delay of 10 minutes, and it's frequency is changed to once per minute.
In either case, the save DC of your Synthetic Venom is equal to 10 + 1/2 your class level + your Int modifier, and it requires one save to shake off the effects.
Poison Use: A Poisoner gets Poison Use at first level. This replaces the Brew Potion bonus feat, which is gained at second level.
Milk Venom: A Poisoner gets Milk Venom as a bonus feat at first level (see below.) This replaces Throw Anything.
Swift Poisoning: A poisoner gets Swift Poisoning at 3rd level. This replaces Swift Alchemy, which is gained at 6th level.
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New Feat: Milk Venom: A character with this feat may milk the venom from a poisonous creature. The creature must either be willing or helpless (alseep, restrained, etc.) Venom may be milked from a dead creature, but only if it has been dead for less that the character's Int modifier in rounds (Undead with naturally occuring poisons are exempt to this rule.)
The character makes a Craft (Alchemy) check against the DC of the poison in question. If the check is successful, you milk 1d4 doses of poison from the creature, and the creature cannot use it's poison for 1 minute. A roll of 1 on this check exposes the character to the poison, unless the character has the Poison Use ability.
Prerequisite: Craft (Alchemy) 1 Rank.
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New Discoveries
Alchemical Bomb: The Alchemist knows the art of preparing and using incendiary bombs. This functions as the Alchemist's Bomb class feature; if the character has another ability that replaces the Bomb class feature, he must divide the uses between the two features (so an Alchemist with Synthetic Venom and Alchemical Bomb, with 5 bombs per day, could prepare 2 doses of venom and 3 bombs. How the two are divided is decided when the Alchemist prepares his extracts for the day.)
Special: An Alchemist with the Bomb class feature may not select this discovery.
Concentrate Poison: As printed, except:
Special: An Alchemist concentrating his Synthetic Venom does not have to use it within one hour; it is inert until it is applied as normal.
Corrosive Poison: This odd poison is tailored to interfere with the workings of constructs, jamming gears and corroding metal and other materials. This poison deals normal Synthetic Venom damage to constructs. Against living targets, they are instead sickened for a number of rounds equal to half the Alchemist's class level, and Nauseated for a number of rounds equal to his Int modifier (if the Nauseated duration would exceed the Sickened duration, they are instead
Sickened for the remainder of the duration.) An Alchemist must be at least 4th level before selecting this discovery.
Dilute Poison: By concentrating for one minute, an Alchemist may dilute a dose of poison (including his Synthetic Venom) in order to stretch it's usefulness. Using this discovery reduces the duration by half (to a minimum of 1 round/minute, depending on frequency) and reduces the DC by 2, but creates a second dose of poison identical to the diluted poison. These doses must be used within one hour or they are rendered inert.
Special: An Alchemist diluting his Synthetic Venom does not have to use it within one hour; it is inert until it is applied as normal.
Hallucinogen: This psychotropic poison interferes with the target's senses. Instead of dealing damage, it imposes a 20% miss chance on all attack rolls for a number of rounds equal to half the Alchemist's class level. Additionally, for a number of rounds equal to the Alchemist's Int modifier, the victim treats all other characters as if they were the subject of a Mirror Image spell with 2 duplicates per subject. An Alchemist must be 8th level before selecting this discovery.
Lambent Poison: More closely resembling a drug than a proper poison, this concoction is laced with positive energy. This poison deals normal Synthetic venom damage to undead. Against living targets, it produces a euphoric feeling that reduces their will save by -2, and an additional -2 for a number of rounds equal to the Alchemist's Int modifier. An Alchemist must be at least 4th level before selecting this discovery.
Paralytic Poison: A more concentrated sedative, this poison does no damage but renders the target paralyzed for a number of rounds equal to half of the Alchemist's class level. Additionally, it requires 2 saving throws for a number of rounds equal to the Alchemist's Int modifier. An Alchemist must posess the Sleeping Poison discovery before selecting this discovery.
Sleeping Poison: Actually a strong sedative and anaesthetic, this poison renders a target quickly unconscious. The target takes no damage; instead they fall asleep for a number of rounds equal to the Alchemist's class level. Additionally, the target takes a cumulative -1 penalty to saves against sleep effects (including this effect) for a number of rounds equal to the Alchemist's Int modifier. This penalty is removed if the character succumbs to the sleep effect.
Synthetic Venom: The Alchemist knows the art of preparing and using a synthesized poison. This functions as the Poisoner's Synthetic Venom class feature; if the character has another ability that replaces the Alchemist's Bomb class feature, he must divide the uses between the two (as Alchemical Bomb, above.)
Special: An Alchemist with the Synthetic Venom class feature may not select this discovery.
Weakening Poison: Designed to 'take the fight' out of it's victims, this poison deals 1d3 Strength damage per round instead of the normal HP damage. Additionally, it deals 1d3 Con damage for a number of rounds equal to the Alchemist's Int modifier. An Alchemist must be at least 8th level before selecting this discovery.
