The Enlightened Scholar class has this particular class menu ability:
Note: I'll break down the requirements in bullet points, so its easier to refer to them. the bold faced ones are in the class menus elsewhere, so they don't need to be dealt with.
(Requires the Clean Living, Craft Alchemical Mixture, Excellent Alchemy, Internal Alchemy, Poison Use, and Poison Immunity class abilities and 2 ranks in Craft (Alchemy))
Poison use is commonplace in other classes (and it hints at forcing the scholar to multiclass) but how to get Craft Alchemical Mixture and Excellent Alchemy baffle me.
Where/how can the ES obtain all the requirements to obtain this ability?
P.S.: Soapbox all you want about the quality of 3PP elsewhere, but not here, not now. Just a good nice old objective stack answer.