Disclaimer: Young Justice is not mine.
Lament—At first, Zatara laments the fact neither he nor anyone else was levelheaded and alert enough to suggest that Nabu possess not Zatanna or Zatara, but one of Klarion's fallen henchmen instead. Oh, how different life would be now if only someone had had that foresight. But the more Nabu listens to—and occasionally acts on—Zatara's advice, the more Zatara realizes just how much power Nabu's host really has. With extreme reluctance, Zatara concludes that this arrangement is probably the best that could be managed after all.
Persona non Grata—It honestly hurts when most of Zatara's acquaintances in the League turn to him and address Nabu as though Zatara is not even there.
Cover-up—The League has always worried about how it's perceived in the public eye. The balance of opinion that keeps the League in a favorable light is a delicate thing, and a tremendously helpful one. It enables the League to wield a measure of influence in municipal and political affairs, and over the years that influence has likely saved scores of lives. That's why the Justice League's founders and leaders—Superman, Batman and Wonder Woman— decide to provide the newscasters with an airbrushed version of Dr. Fate's back-story instead of the real thing. Zatara can't disapprove of Superman's, Batman's and Wonder Woman's decision. Giovanni has no wish for Nabu's inclusion to taint the League's reputation.
Glimpse—Rarely, Zatara sees his daughter out of the corner of his eye. Zatara is a proud man, but in these moments he pleads with Nabu to look in Zatanna's direction.
Solace—Despite Zatara's banishment into the helmet, a few people still talk to him. Captain Marvel makes sure to speak about how Zatanna is doing, while Dinah tells Zatara about her day and fills him in on anything Captain Marvel didn't mention. Wonder Woman—Diana—makes conversation with both Nabu and Zatara. Diana explains that, as strongly as she objects to Nabu's methods, she will not take the easy path of condemning him out of hand. Instead, she wishes to talk to him so that they can both gain a broadened perspective. Zatara is surprised by Diana's decision, but then, Wonder Woman has always favored diplomacy whenever possible.
Sacrifice—Zatara has suffered extensively because of his choice to take his daughter's place as Nabu's host. Zatara is cut off from the world, restricted to a small space within the helmet. He cannot control where Nabu takes his body, what sights and sounds the Lord of Order chooses to give him. Zatara can no longer taste food, and he can barely smell anything. Worst of all, Zatara is deprived of the ability to talk to people, be they enemies, associates he can barely stand, pleasant acquaintances, treasured friends, or his only daughter. Zatara's existence is truly hellish—and whenever he thinks of Zatanna, Giovanni is relieved he made his bargain with Nabu. Suffering this torture himself is bad enough, but the thought of Zatanna going through it—Zatara can't finish the thought.
Replacement—Watching Nabu step through the Zeta tubes and hearing the computer announce "Dr. Fate" instead of "Zatara" stings badly for a while.
Pointless—Zatara finally gets Nabu to relate the details of his two prior encounters with Batman's "Team". Afterwards, Zatara could almost weep with frustration. First, an unofficial mission from Red Tornado that wound up pitting the Team against two very strong enemies. Second, Batman's stupid, arrogant decision to send his overmatched Team into battle against seven powerhouses. Two times Dr. Fate wound up being needed, two times that never would have happened without Justice League ego.
Small-talk—Zatara tries, on occasion, to strike up conversation with Nabu. To both their surprise, they manage to learn a bit about each other. Zatara played chess religiously in his teens and had aspirations of becoming a grandmaster for a living before focusing on magic instead. Nabu has always desperately wanted to play Monopoly, but he has never managed to find anyone willing to do a game with him.
Unnerved—Zatara's primary reason for convincing Nabu to join the Justice League was so that the League could keep a close eye on Dr. Fate. Zatara was relieved when he managed to sell Nabu on the idea of teaming up with other heroes, and he was thankful Batman, Superman and Wonder Woman accepted this reasoning during the initial, private meeting on the possibility of Nabu's induction, but that didn't mean the rest of the Justice League needed to be so blasé about Nabu's membership. If Captain Marvel hadn't questioned Fate's admittance to the Justice League, Zatara wonders if anyone besides Dinah or Green Arrow would have said anything at about it at all.
Ulterior—Together, Nabu and Zatara have many reasons for being a part of the League. For Nabu, the League is an opportunity to pool the talents and viewpoints of multiple heroes to better keep Order in the world. For Zatara, the League is a method of hopefully keeping Nabu's behavior in check. Lastly, though neither of them will admit it, the Justice League is a chance to be around people and listen to them talk, even if they can't speak up in return.
Sub-Standard—Zatara is relieved that his daughter will be well-cared for in his absence, but he wishes that Batman hadn't brought Zatanna into the Team in the process. Zatara has plenty of friends who are able and willing to give Zatanna a new home. The Team isn't Zatanna's only option, and it's definitely not the safest. All of those children are taking their lives in their hands almost every time they go on a mission, and now that Zatanna's home is here, she has no alternative to being a part of that as well. Zatara always wanted Zatanna to have the freedom to choose what happened in her life. (It's an ironic sentiment from such a protective father, but true all the same.) Now Zatanna has lost that freedom. As long as she's under Batman's legal guardianship, Zatanna will never be able to quit being a superhero without walking away from the only family she has left. It's possible this is all just some fucking oversight and not a deliberate attempt to manipulate his daughter, but Zatara is furious at his old friend either way.
Escape—Zatara has all the time in the world to examine his prison inside Nabu's helmet. The floor feels like rough stone. There are no walls. The light shines from a ceiling Zatara can't see. Zatara attempts to cast a spell, but he can't even feel a grip on his magic. It belongs to Nabu now. The overhead light follows Zatara as he tries walking around, but there are no landmarks, and after an hour it feels like Zatara hasn't gotten anywhere. In desperation, Zatara stomps the ground with his foot. It doesn't do anything, but Zatara rips his shoe off in a rage and bangs it against the ground over and over. Zatara's body doesn't tire in this place, but eventually his anger cools and he sags to the floor, weeping. Nabu must be able to sense this through their link to each other, but the Lord of Order mercifully says nothing.
Humor—In retrospect, Hawkwoman's joke is good, but probably not quite as funny as it seemed at the time. Zatara isn't sure whether he or Nabu is the first to start chuckling, but soon they are both laughing hard. Zatara eventually realizes the League is staring at Nabu, and that Nabu is snorting through the helmet. Zatara dutifully attempts to stifle his mirth while Nabu belatedly composes himself before the League.
Apology—Nabu's presence appears within Zatara's prison. Zatara waits for Nabu to speak, but the Lord of Order says nothing for a long moment. Finally, Nabu reaches out with his mind and sends…impressions into Zatara's head. Zatara receives images of pristine, achingly beautiful Order; of almost impossibly noxious Chaos; of aeons-long duty; a measure of weariness, a slight loneliness; and a faint sense of…guilt? Nabu offers nothing more. Zatara sighs. Nabu's motivations have never been much of a secret from him. Nabu is a Lord of Order. It's in his nature to combat Chaos relentlessly and with little compromise. And in truth, if being Nabu's host is hell for Zatara, being without a host must be an even worse hell for Nabu, despite his stoic endurance. At least Zatara can still see and hear the world outside. At least Zatara still has Nabu's erstwhile company to stave off complete isolation. Without a host, the ability to relive his memories and his patient meditation are Nabu's only defense against boredom and madness. Zatara honestly almost pities the Lord of Order sometimes, but that doesn't mean Zatara can forgive him.
Future—Zatara will not stay young forever, so there is the possibility that Nabu will one day release him. Zatara clings to that hope like a lifeline, but he still wonders what he will do with the helmet if that day ever comes. Should Zatara render the helmet unusable, depriving the world of its power but guaranteeing that no one else will give him- or herself up to Nabu? Out of the question. Terrible as the Helmet of Fate is, the power within still has ability to turn the course of an otherwise lost battle.
…Besides, despite Nabu's cruelty in taking his body it would be unfair of Zatara to consign him to death or oblivion.
Should Zatara seek out a new host and persuade him or her to accept Nabu? How can Zatara ask another to endure such a torment?
Could Giovanni or the League find a criminal and emplace the helmet by force? That solution is almost perfect, but Zatara has managed to use his position as Nabu's vessel to influence Nabu before, and if Zatara can do it, what's to stop a helmet-possessed villain from doing the same thing?
Service—Unlike some of the League members, Zatara has always found looking over sensor readings to be relaxing. Sensor monitoring simply calls for observation. Nothing beyond that is required. Though others of the League find that inaction unpleasant, Zatara enjoyed just standing and looking.
After Nabu co-opts his body, that duty becomes even more calming. There's no locomotion involved, so Zatara isn't watching someone else pilot his body. There's usually no socializing involved either, so Zatara doesn't have to endure people looking at his face and talking to Nabu. There are only the monitors, background noise, and the job at hand. It's just like old times. Sometimes, Zatara even allows himself to pretend that nothing has changed.