QMy opponent has an evolved Ginsetsu, Great Fox and an evolved Shuten-Doji on their field, and they attack my leader with the latter. I play this spell at quick timing, giving the evolved Shuten-Doji -2 attack and defense. Since the evolved Ginsetsu, Great Fox's ability increases Yokai followers' damage dealt by 1, does my leader take 1 damage?

ANo. A follower with 0 or less attack doesn't deal damage, and Ginsetsu, Great Fox's "if a Yokai follower on your field would deal damage, it deals that much plus 1 instead" only takes effect when damage is dealt.

QCan a follower have negative attack?

AYes. A follower's attack can be reduced to a negative number by effects. A follower with negative attack doesn't deal attack or combat damage.

QCan this spell's activated ability only be played while it's in the cemetery?

AYes, that's correct.