So, I've been working on some custom rules and what not recently. As part of this process, I've been attempting to review a variety of baseline RaW so as to understand the framework as a whole better, and therein more effectively inform my extensions 
. Ironically (to me, anyway), I've found that a great many rules I thought were RaW, or at least, thought were addressed in RaW I haven't been able to find. To whit, I remember reading once upon a time rules governing how mystical creatures could increase their Might ("permanently"). That said, I haven't had any luck finding those rules. I thought RoP:M was the place, but I haven't found it. I have physical books, not pdfs, so searching is not really possible . Can anyone point me to the appropriate source/section/page?
Pages 52 of RoP:M give rules for advancing by gaining new Qualities/Inferiorities through Transformation. Any Minor Qualities gotten could be used on Improved Might, which would (permanently) raise the creature's Might score. It's not a fast process by any means, but it is in fact a thing you can do. That said, that only really applies to Magic creatures. Faerie, Infernal, and Divine beings have their own rules related to advancement.
RoP:M -> Transformation, adding Increased Might
RoP:F -> Get an artist to assist in manipulating your glamour so you can spend experience to add the Faerie equivalent to Increased Might
RoP:tI -> Not sure, but I think you can fight your way up the hierarchy. Also, Ablating can increase Might.
RoP:tD -> I think God has chosen the values, but some do increase over time like those half-divine people who get really big and age slowly.
(All protected by serf's parma.)
All of the above.
TMRE: Daemons can increase might through vis offerings. Other magi who use mysteries+magic can recast the mystery spells or recreate alchemical potions at a higher level.
MC: Bjornaer Great Beasts who manage to gain xps in their Heartbeast ability get a higher Might. (Inferred.)
Well, Transformation, in and of itself does not increase Might. The Magical Quality, though, I will have to check. Seems a little counter intuitive to me that you get xp then use it to buy up your Might as opposed to buying up other qualities, given how qualities are generated in the first place. But if that is the only RaW mechanism, that's what I wanted to know . I'll check on the other references as well.
Improved Might explicitly doesn't let you get more Qualities, in case that inconsistency is still bugging you. Other than that, what's confusing? There's a Quality that increases your Might and you can get new Qualities through Transformation, so there's no need for a separate Might-buying mechanism.
Daimons can also increase their Might through worship and Pacts, which is a form of transformation.
Add to RoP: Magic - Magic Things (Elementals, and other inanimated things with Might) can add to being part literally or symbolicaly of other greater, adding mass.