Ok...I have a couple questions on teh Aeons. Are you intending this to be a player behind the controlls, assuming if you are it would be the summoner that is controlling the Aeon, correct?

Also, any chance we'd get to see some of the FFX Aeons worked up in this mold like Valefor, Ifrit, Shiva, ect...

Also, I Know this is set up to get the Aeons in line with other, "normal" classes since the rest of the party will be out there too...but these just seem very weak compaired to the Aeons in the game unless some of your origonal character abilities have effect on your Aeon form. Again, this is all running on assumption so if I'm invisioning this wrong, tell me to STFU and ya won't hurt my fealings :)

When you, or whoever, become an Aeon I assume you automatically take on the Aeon monster class, correct? What I would do is set the Aeon classes BAB against the origonal creatures BAB. Yes, that would require another chart, but luckly I don't think any of the Aeon had Bad BAB, just mediocre. So, I'd say that if your "Base" BAB was either poor(Wizard ect...) or Medium(monk ect...) you get Median BAB, where as if you had full BAB(Fighter) or or had multied and had better than median(Monk/Fighter cross class) you get Full BAB as an Aeon.

Also, not all Aeons were good casters. In all honesty Ifrit, Valefor & Ixion sucked on their basic spell progressions/selection. They either had low damage output on spells(Valefor) or had a low selection of spells to choose from(Ifrit/Ixion and also Jecht). I'd put in a caviat in the ritual that a basic Aeon monster class has an amount of MP based on his Hero classes. If a character had a full caster class(Wiz/Sorc/Cleric/Druid/ect...) and became an Aeon they'd have the full MP progression listed above. But if they were a partial or non-caster, their MP progression would be cut to, say 5d4 + 20 instead.

One other question, this time more relating to the ritual it's self. It looks like this is meant to be a PC that comes up and sacrifices his character(bored with it, can't keep coming, ect...) to become an Aeon. Will this work with Cohorts from the Leadership feat? Can your cohort "decide" (s)he want's to become your Aeon and allow you to perform the ritual on them? If not, you might want to clarify where the host person for the Aeon comes from, be it a Diplomacy check with a group of people, or what have you.

Sorry to chew your ear off. I love what you have so far, just some thoughts that came to mind when I saw the class.