combat casting feat question

[Valeria]

Is anyone familiar with this feat?  If so, I was wondering two things:

1) what spells, "not usually castable during combat", does this apply to?  Sanctuary? Paralysis? Change form? Ironskin/Harden? etc.

2) is it really a 50% of the time success or so?

Thanks for any insight on this feat!

[deda]

Every spell can be cast in combat, you just have to spam... Never tried shapeshifting, cause i don't use forms being an abjurer... the percentage? I'd say it's even below 50 but I still haven't mastered combat spellcasting, so i guess I may be wrong...

[Akhulas]

all except shapeshift