Right.
Advanced Player's Guide wrote:
evolution surge: This spell causes your eidolon to take on new characteristics. You can grant the eidolon any evolution whose total cost does not exceed [2,4,6] evolution points. You may only grant one evolution with this spell, even if that evolution can be taken multiple times. You can grant an evolution that allows you to spend additional evolution points to upgrade that evolution. This spell cannot be used to grant an upgrade to an evolution that the eidolon already possesses. The eidolon must meet any prerequisites of the selected evolution. This spell does not allow an eidolon to exceed its maximum number of natural attacks.
I have a bunch of questions, because while this spell is transmutation, it's not in the polymorph subschool. Let's talk about what happens when you grant the Large evolution.
1) I know this has been asked before, but what happens to the Ability Increases you've already purchased?
2) While the Large evolution grants size bonuses, what's another good polymorph spell that can add to this one? (more of an advice question, sorry)
3) When you go from Medium to Large, it doesn't say anything about the eidolon's gear growing either. Does this mean that (say), the eidolon's belt of giant strength snaps off during the surge?
4) So, you can't upgrade an evolution that you currently possess (no going Huge with greater evolution surge). However, even though your surged evolution only lasts minutes, could you spend real points to upgrade spell-given points? Here's an example:
a) cast evolution surge on your eidolon, making it Large.
b) somehow cast transmogrify with a standard action, instead of the usual 1-hour casting time.
c) Can you shuffle the points around so that the first evolution surge spell is the one that grants Large, and then you spend 6 points yourself to grant Huge.
