Board Thread:News and Announcements/@comment-72.10.66.17-20130919181636/@comment-3250527-20150201025651

hConcealment crystal..... no, SAO already has a «Hiding» skill. If you can't utilize that, then you're not hiding correctly.

The Yellow crystal is not going to be elaborated on, unless it makes an appearance in the Progressive arc. That being said, the yellow crystal will be up to that person's imagination.

(Since I'm making an SAO fanfiction, I made my Yellow crystal have flashbang properties. No copy pasterino.)