its indeed spellbook is one copy per turn but not at star hall, starhall is +counter (if you suggesting citadel), +atk, and +add, just destroy it with MST or heavy storm when it has counter (3 is enough) then add exodia with this eff, 3 star hall is +3 i think, first i used citadel, but when i used it, library only can use citadel's counter once per turn even citadel has more than 3 counters after first use(maybe bug, and i've deleted my replay, i'll test it again and post the replay if i has same problem again), so i changed with tower, i'll test what your suggest tho, coz i want improvement (fastest now is 4 turn exo), so why not
Here's how to pick, the top five, and the math behind it
the equipped monster gains ATK equal to the sent monster's ATK, until the end of this turn (even if this card leaves the field)
Kastral ignores the concept of feather counters and instead deals in +1/+1 and finality counters
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