What fun mechanics can I use for TSOY magic?
* Secrets, as written (as per the words of Zu/Uz).
* Unlockable secrets and/or secrets that have prerequisites (Secret of Elements > Secret of Fire, Air).
* Secrets that unlock abilities (Secret of Psionics lets you buy the Telepathy ability).
* Abilities, and abilities that unlock or have prereqs (everyone can buy Telepathy, no Secret required).
* NPC spirits bargained with or exploited.
What else is out there?