The wording is confusing when you combine the concept of the 'rage mutagen' with that of the greater and grand mutagens, and there are several possible sets of numbers one could end up at.
Luckily, this can all be posed to the developers as a fairly straight forward question. Hopefully we can get some feedback as I have seen this question appear and disappear several times and am currently playing a Ragechemist myself.
What are the possible Mutagens and/or Rage Mutagens a level 12 Ragechemist possessing the Greater Mutagen discovery can make and what are their total effects?
What are the possible Mutagens and/or Rage Mutagens a level 16 Ragechemist possessing the Greater and Grand Mutagen discoveries can make and what are their total effects?
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For what it is worth, my understanding of RAW would let a level 12 Ragechemist make a greater rage mutagen providing...
+6STR(alch), +6DEX(alch), +2CON(morale), +4NatA,-2INT,-2WIS. Failing the will save from damage in a round is -4WillSaves, -4INT, -1DEX. The base mutagen before the rage modifer would have been +6DEX,+4STR,-2WIS,-2INT
or...
a greater rage mutagen providing +6STR(alch), +6CON(alch), +2CON(morale), +4NatA,-2WIS,-2CHA. Failing the will save from damage in a round is -4WillSaves, -4INT, -1DEX. The base mutagen before the rage modifer would have been +6CON,+4STR,-2WIS,-2CHA
or...
a standard greater mutagen providing either a +6CON/DEX(alch) and +4DEX/CON(alch) with the normal -2 to associated scores. Unaffected by rage mutagen changes as the mutagen does not affect the alchemist's strength.
or... this one takes a RAI approach.
A greater rage mutagen as described above that provides +8STR(alch) and +4DEX/CON(Alch), +2CON(morale), +4NatA, -2INT, -2WIS/CHA. Failing the will save from damage in a round is -4WillSaves, -4INT, -1DEX. The base mutagen before the rage modifer would have been +6STR,+4DEX/CON,-2INT,-2WIS/CHA.
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My RAI take is that any mutagen affecting the alchemist's STR is a Rage mutagen and has its +#STR(alch) replaced with an alchemical bonus to strength 2 points higher; the alchemist also receives the penalties associated with a rage mutagen. If the alchemist is level 6 or higher, or 10 and higher, further apply the changes from Sturdy Rage, and Lumbering Rage as appropriate.