Sorry in advance for the wall of text. My idea here takes inspiration from a lot of suggestions I've seen on the forums, along with some personal ideas. The goal here is to help ease the RP cost burden on the alchemist, in order to let them actually keep up with their comrades, and to give them their own unique niche as a gadgeteer master. I also listed 4 specialties for the alchemist, mimicking how the druid and bard are set up, to allow individual alchemists to choose what to focus on. My ideas are:
Change infused trait to negate the RP cost of activating the item, period.
[1st] Advanced Alchemy:
Change the bit about spending RP to make half batches of items to:
By spending 10 minutes, an alchemist can create a number of alchemical items equal to their Int modifier (minimum 1 item), ignoring the usual crafting time and material cost. An alchemist may have only up to their int modifier crafted this way at a time, but can otherwise use this ability as many times a day as they like. An alchemist is free to render any unused items they craft with this ability inert as a free action; making the item useless and freeing up space from their limit.
Quick alchemy is fine as is, RP cost and all.
//This solves the sustainability issue with the alchemist by simply giving them an out of combat way to keep on manufacturing items. Alchemists will still want to put some thought into how they use their items, but they will find themselves with a respectable amount of options in encounter and exploration mode, and can restock their goods by using a turn in exploration mode. It lends a feel to a gadgeteer who uses good prediction and problem solving to help their team.
[1st] Alchemical Resonance (replaces Studied Resonance):
You gain a pool of resonance points equal you int modifier plus half your alchemist level (rounded down). These points can only be used for Quick Alchemy. This is in addition to your normal RP pool.
//Some may not like this, as cha is no longer true a dump stat, but this ability should really be thought as a pool of "spell points" to fuel Quick Alchemy rather than a resonance pool. Furthermore, both Goblins and Gnomes, arguably two on the most alchemy friendly races, flavor-wise, boost cha, so may as well let them see some small boon for that.
Change Precise Bomb to a 1st level alchemist feat
//friendly fire negation is extremely important to how an alchemist functions, and it's unfair to punish them by making them wait until 6th level before they can actually use their main tool
[3rd] Research Field (replaces Empower Bombs)
At third level, an alchemist chooses a specialty field of alchemy to pursue. Each research fields gives the alchemist a free alchemist feat at 3rd, 7th, 11th, 15th, and 19th level, ignoring their usual level prerequisites, based on their chosen focus. The level a specialist gains the feat is listed in parenthesis, the level any other alchemist can select it is listed in brackets. The available fields are:
Demolitions - A field that specializes in explosive alchemical reactions. Demolitions focused alchemists lob devastating bombs in combat to inflict great damage to their foes. The feats they get are:
(3rd) -[4th] Empower bombs +1:
Bombs created by the alchemist get a +1 item bonus on attack rolls, and one bonus damage die. Bombs that do not have a base damage, but still inflict persistent damage (such as Acid Flasks) instead have the bonus damage die added to their persistent damage (so an acid flask would deal 2d4 acid damage per cycle). Bombs that do not deal damage at all still get an item bonus on attack rolls, but do not benefit from damage enhancement. The alchemist gains Expert proficiency in Alchemical Bombs. Bombs created by the alchemist that benefit from this feat are considered to have a crafting level equal to the alchemist's level.
(7th) -[8th] Empower Bombs +2:
Requires Empower Bombs +1
As Empower Bombs +1, but the item bonus is increased to +2, and adds 2 bonus damage dice. At level 8, the alchemist may add the lesser version one of the following of the following property runes to their bombs: Corrosive, Flaming, Frost, or Shocking. At 14th level, they may add the greater version on these runes instead.
(11th) -[12th] Empower Bombs +3:
Requires Empower Bombs +2
As Empower Bombs +2, but the item bonus is increased to +3, and adds 3 bonus damage dice. The alchemist adds Anarchanic, Axiomatic, Holy, or Unholy to the list of runes they may apply to their bombs. The alchemist gains Master Proficiency with Alchemical Bombs.
(15th) -[16th] Empower Bombs +4:
Requires Empower Bombs +4
As Empower Bombs +3, but the item bonus is increased to +4, and adds 4 bonus damage dice. The alchemist may add 2 property runes, and adds Speed to the list of runes they can add.
(19th) -[20th] Supreme Bombs:
Requires Empower Bombs +4
As Empower Bombs +4, but the item bonus is increased to +5, and adds 5 bonus damage dice. The alchemist may add 3 property runes to their bombs and gains Legendary proficiency with alchemical bombs.
//the idea here is to make bomb damage and accuracy scale the same way an enchanted item does, to keep a bomber's damage on the same track with a martial's attack. The reason being is that while the alchemist may be more versatile, the fact that they are limited to, at most, 10 or so "free" bombs (and this includes the alchemist maxing out the next proposed feat list using class feat selections) without using quick alchemy, balances them to the more focused martial. The idea of alchemists being able to make bombs that ignore energy resistance via greater elemental runes is also really cool and unique, and emphasizes the gadgeteer motif
Apothecary- Alchemists who follow this field are experts at crafting a diverse array of items to solves problems. While not as flashy as the other fields, apothecaries are welcomed in most towns and adventuring parties due to their helpful talents. The feats they gain are:
(3rd)- [4th] Alchemical Expertise +1:
The alchemist increases the item bonus provided by any set of Alchemist's tools they use by +1. The alchemist also treats their int modifier as 1 higher for the purpose of Advanced Alchemy.
(7th)- [8th] Alchemical Expertise +2:
Requires Alchemical Expertise +1
The alchemist increases the item bonus provided by any set of Alchemist's tools they use by +2. The alchemist also treats their int modifier as 2 higher for the purpose of Advanced Alchemy.
(11th)- [12th] Alchemical Expertise +3:
Requires Alchemical Expertise +2
The alchemist increases the item bonus provided by any set of Alchemist's tools they use by +3. The alchemist also treats their int modifier as 3 higher for the purpose of Advanced Alchemy.
(15th)- [16th] Alchemical Expertise +4:
Requires Alchemical Expertise +3
The alchemist increases the item bonus provided by any set of Alchemist's tools they use by +4. The alchemist also treats their int modifier as 4 higher for the purpose of Advanced Alchemy.
(19th)- [20th] Alchemical Mastery:
Requires Alchemical Expertise +4
The alchemist increases the item bonus provided by any set of Alchemist's tools they use by +5. The alchemist also treats their int modifier as 5 higher for the purpose of Advanced Alchemy.
//This might seem like the boring-but-practical choice, but clever players can find many ways to take advantage of having extra slots. The synergy with Tricky Tinker, and other possible future feats, is very much intended. This is the versatility chain.
Toxicitian - Alchemists who specialize in the study of poisons and venoms. Many treat alchemists of this field with suspicion and fear, though people with more dubious morality often seek their services. The feats they gain are:
(3rd)- [4th] Poison Expertise +1
Poisons created by the alchemist use their class DC as the save DC, if higher than the poison's normal save DC. The alchemist gains a +1 item bonus to their class DC for this purpose when using a poison with the infused trait.
(7th)- [12th] Poison Expertise +2
Requires Poison Expertise +1
As Poison Expertise +1, but the item bonus is increase to +2.
(11th)- [12th] Poison Expertise +3
Requires Poison Expertise +2
As Poison Expertise +2, but the item bonus is increase to +3.
(15th)- [16th] Poison Expertise +4
Requires Poison Expertise +3
As Poison Expertise +3, but the item bonus is increase to +4.
(19th)- [20th] Poison Mastery
Requires Poison Expertise +4
As Poison Expertise +4, but the item bonus is increase to +5.
//simple, but those save DC bonuses can get real nasty. I didn't see much need to buff other aspects, due to the fact that later level poisons can get very nasty, damage and effect wise, and the save DC increases make it really hard to recover, except maybe with the aid of an equally skilled alchemist :)
Mutagenics- Alchemists who follow this field focus on the powerful potential of mutagens. Most of society regard them as mad scientists, but adventurers welcome their unorthodox methods. The feats they get are:
(3rd) -[4th] Lesser Mutagenic Form
When gaining this feat, the alchemist chooses one type of lesser mutagen, and once chosen, cannot be changed, without extensive and difficult retraining. In encounter mode, the alchemist may use an action to gain the benefits and drawbacks of the selected mutagen for three rounds. In exploration mode, this duration is increased to 10 minutes (effectively lasting for the duration of one tactic), but is reduced back to 3 rounds should the alchemist enter combat mode. feats that modify the effects of mutagens (such as feral mutagen) also alter the effect of Mutagenic form, if the alchemist's chosen mutagen is of the corresponding type.
(7th) -[8th] Mutagenic Form
Requires Lesser Mutagenic Form
Same as Lesser Mutagenic Form, but the benefits are increased to the regular version of the chosen mutagen. The drawbacks do not change. Effects in encounter mode last for 4 rounds
(11th) -[12th] Greater Mutagenic Form
Requires Mutagenic Form
Same as Mutagenic Form, but the benefits are increased to the greater version of the chosen mutagen. The drawbacks do not change. Effects in encounter mode increase to 5 rounds, and 20 minutes in exploration mode.
(15th) -[16th] True Mutagenic Form
Requires Greater Mutagenic form
Same as Greater Mutagenic Form, but the benefits are increased to the True version of the chosen mutagen. the drawbacks do not change. Effects in encounter mode last for 6 rounds.
(19th) -[20th] Mutagenic Mastery
Requires True Mutagenic form
The alchemist may change the type of Mutagenic Form they adopt by taking 10 minutes to alter their body's biochemistry. This requires alchemist's tools, and if the process is interrupted, the alchemist must start again from scratch.
//The idea here is to capture the feel of the master chymist from the first pathfinder game, along with iconic characters of a similar nature, such as the Incredible Hulk, or even "smart drug" users, if the mutagen chosen was the cognitive mutagen. The main reasons I made the drawbacks not scale is that for effects like the Bullheaded Mutagen, that costs RP, or Quicksilver, which costs HP would result in unfair punishment on resources compared to the bestial mutagen, which only have a -1 to a handful of skills throughout its entire progression, and would not tax resources at all.