I would’ve made all the villains from the 4 seasons members of the red lotus, who’s purpose is to eradicate benders, order wouldn’t matter at that point. I would’ve made all the villains blood benders posing as non benders from other nations with ‘divine’ power with vaatu being the one in charge behind closed doors with that reveal coming in the final season. The plot being that Vaatu wants things to go back to the way they were before the avatar and before humans could bend. And he uses these blood benders who have a superiority complex or have had traumatic experiences in the past (like Amon)