[K Peculier]

Arcane Formation will not effect magical spells from youkai both that are evoked and from the youkai itself if you are standing in Arcane Formation or have it filled.

Magical spells from other classes such as mage will effect your spell power however.

[Neus]

What skills are you testing this with?

[Ranylyn]

Unless it was changed post-GR, nothing that boosts spells (tomes, etc) affects Youkai spells. They're simply counted as spells so they can be silenced.

[K Peculier]

I had used the drowned woman and seiryuu magic spells while on the arcane formation and they do not work. Not quite sure about all of them however.