also, SE writers take note if you didn't do this, but the ultimate tone-setting plot device for a shocking moment would be
(lv80 sharlayan spoilers) the flower that changes colours based on emotions. the group is all happy after some event... the world has been saved, there's absolutely no reason to be concerned anymore... the flower is happy-coloured... and then all of a sudden... it turns dark for some reason. someone nearby, someone we trust... is feeling deep hatred... insert plot twist of someone revealing themselves to be a villain here, or etc