How do you get advance enchanment?

It only comes from the above listed bosses, or gachapon (well, atleast it did come from gachapon, I'm not sure if it was removed though). You cannot get one from saving miracle cube pieces. It's different in that it starts with a 20% higher chance ato succeed than a normal enhancement scroll, though it still drops down to 10% success rate eventually. So the Advanced Enhancement goes: 100%, 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, 10%... So the first use is a guaranteed success; once you've passed 9 enhancements though it's the same probability of success as normal enhancement scrolls.