RAW, can a Mnemostiller Alchemist learn the Fey Mutagen Discovery?
Relevant Text:
Benefits: You gain the ability to create a fey mutagen.
When imbibed, a fey mutagen grants a +2 alchemical bonus to the alchemist’s Dexterity and Charisma, a –2 penalty to his Strength, and DR 2/cold iron. This otherwise works like the standard mutagen class feature and interacts with other effects as though it were a mutagen.
A mnemostiller learns to brew a unique type of mutagen, called a rasugen, that suppresses his mind to enter a state of sublime purity. In this state, a mnemostiller becomes incredibly resilient, but cannot perform complex skills. Once imbibed, a rasugen grants a +2 alchemical bonus on all saving throws and 2 temporary hit points per alchemist level for 10 minutes per alchemist level. In addition, while the rasugen is in effect, a mnemostiller takes a –2 penalty to his Intelligence score and can’t attempt checks using Appraise, Craft, Disable Device, Heal, Knowledge (any), Profession, Sleight of Hand, or Spellcraft. This acts in all other ways like a mutagen.
This replaces mutagen. A mnemostiller can never gain the mutagen, cognatogen, or inspiring cognatogen ability, even from a discovery or another class.
Bump.
I'm guessing most GMs (and Paizo) would say this:
1.) The Mnemostiller cannot gain the mutagen ability.
2.) Fey Mutagen interacts with other effects as though it were a mutagen.
3.) ???
4.) The Mnemostiller cannot gain the Fey Mutagen discovery.RAI, I doubt it. RAW I think so, but only because the Fey Mutagen is not the specific mutagen, cognatogen, or inspiring cognatogen abilities that are barred.
Oddly enough, the Fey Mutagen came before the Mnemostiller archetype, so I think the designers either thought the archetype's wording was clear enough that specifically calling out the Fey Mutagen was unnecessary (likely) or they forgot about the discovery when writing the archetype.
I think you're overestimating how much any given Paizo employee is aware of the contents of every rule published in every line, especially those in development and not yet published. Freelancers have no hope at all when it comes to things under development, leaving individual book developers to catch any such issues. And player companions never really worry too much about busted rules or weird rule interactions in the stuff they put out there.