The reverse-foil pattern is also different than it was from previous sets, although this tends to change rather often, so its not particularly surprising
The first 3 sets will release on October 28, 2022
As some commenters have suggested, this is almost like replacing your health bar with a sanity meter, and it's a fitting effect to represent a powerful but perhaps deadly tome
Brainstorm might average two cards per 60, but the most popular number for the standout manipulation spell is four
In addition to the ones available via the Pokmon Centre, I remember some being distributed at the actual museum event (and some were packed in with mini-files, though I am not sure if all five cards were available that way)
While Sub-Grades have a small group of loyal fans, over time they have become far less popular with submitters