I've noticed that the online guide for the proof of skill mastery (items you need to master a skill) is out of date. The guide is accurate up to Wicked Flame which does indeed require Quiem Card to master. From then on, however, it no longer holds true. Well that is my experience so far.
After finishing Oops Wharf, i was just about to learn Dark Lance for my Magician. I did make it a habit to collect all the items i need in one place so i won't have to waste time in the future going back for it, especially in the distant future where the monsters that have them give little to no EXP. The next skill to master after the Wicked Flame was Dark Lance which was then not yet ready to be mastered, and therefore i cannot check it with Magician Louie for the requirements. So i head over to guide who said Dark Lance needed 26 Fried Eggs. Along with 7 Aristocratic Fan for Gravity Crush and 10 Malachite for Dark Barrier. Unbeknownst to me that those were old requirements. The new requirements were that:
Gravity Crush requires 3 Okto Cards which can also be found in Mermaid Dungeon.
Both require 3 TM points each to master.
So far, that's all i know, I've just learned my Dark Barrier skill, and therefore i cannot check with Louie for its mastery requirements. I will be updating this skill mastery guide towards the dark side, though anyone with greater knowledge is invited to pitch in!
I dunno how much this helps anyone who's just starting out (if there actually are anyone who's just starting out) but i was hoping we can share information to help each other.