when fiendish chain is activated to target a bujin monster bujingi turtle is activated to negate the effect, however fiendish chain negates the effect of the monster anyway, whilst bujingi turtle does not destroy the card it negates the effect, meaning fiendish chain would be left on the field however it would not negate the effect of the bujin monster
cards cannot be chained to gwenhwyfar queen of noble arms dark-monster-related, equip effect, where it can destroy itself to destroy the monster that the monster it is equipped to is battling.
subterror final battle does not prevent the negation of subterror cards. subterror behemoth ultramafus' effect was activated to flip itself facedown after subterror final battle was activated previously in the turn and not in the same chain, however solemn strike is chained to the ffect, negated the effect, and destroys the monster