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Danny was definitely not expecting Damian to ask what he thought about pulling a prank on their birth father. The Waynes had apparently never been told about Damian's twin that had been sent far away from any and all League businesses from the moment he took a breath.
Dami had defended himself by saying stuff about how the fact that father had had another child whom he's never met just never came up. They seemed to shy away from talking about where Damian had grown up, which included him secretly keeping in contact with his twin.
After Damian had been taken in by their father, he began to text with Danny far more often as he never had to worry about getting caught and Danny getting killed anymore, which was pretty nice. When Danny died Damian was the first to get the full story about everything, followed by Sam and Tucker. Damian and Danny knew everything about each other, even though they lived in completely different worlds. Danny knew everything about the Bat's, including how emotionally repressed all of them are.
So, when Damian wanted to go on a road trip, he asked Danny to take his place in the manor for the 2 weeks he was supposed to be gone. He didn't want any of his brothers to stalk him while he was away. Danny had gleefully accepted. Under the condition that for every blatant lie he got everyone to fully believe Damian had to spend a day with him and the Fenton's. Jazz was upset that she'd never met Danny's twin. His parents, and more importantly Jazz, were all for this, even if it meant sending Danny away for almost a month.
He made sure to spend a week in the manor while invisible to get a better sense of how people interacted with each other, especially how Dami talked to his brothers and their father. If Danny didn't mimic his twin brother perfectly then their whole plan was over before it started.
Danny already knew that this would be a challenge because of how different his and Damian's personalities are, despite looking identical. Luckily because of being Phantom he didn't have to worry about struggling with the physical aspects of being Robin, or the lack of sleep it caused.
This was going to be a fun 2 weeks. Danny just had to start thinking up some sort of lies to get Dami's family to believe. Which will be easier than he thought as Dami has absolutely 0 social skills and doesn't see the point in lying. Sure, he knew that growing up somewhere like the league made Dami as emotionally stunted as their birth father, but with how he acted when he was calling or texting with Danny, he would have thought that the social incompetence had lessened, at least a little. But nope. He's the epidemy of awkwardness.
During day 1 Danny focused on simply not being detected by anyone. Which went really well. For a group of great detectives and vigilantes Danny was a little surprised to find them not batting an eye at him. He waited until day 3 to see about adding in a lie, he started out really simple to test the family.
"Alfred's cooking is a lot better than Ra's cooking" he said during dinner, it was only Bruce and Tim at the table with him, as everyone else had one thing or another to do instead of eating dinner as a family. Bruce seemed to just accept this bit of new information and kept eating after a slight pause. Tim however looked a little shocked, "Ra's never cooked though?" Danny faked a very confused face, "Yes he did Timothy, you were never allowed in the kitchen so you may have not noticed it as he didn't cook very often. He was horrible at it" It took a few minutes before Tim seemed to come to terms with his new reality and continue to eat his dinner.
He waited 2 days before deciding to say something again. His comment about Ra's cooking hadn't been brought up by either Bruce or Tim. This time he was with Jason. The hardest part of this was to have to deny himself the pleasure of straight up asking if Jason would break into Arkham with him to kill the Joker, as Dami abided by Bruce's no killing rules. Danny, however, had no such wish to abide by that specific rule, there are some people who truly do need to be killed to ensure that they don't cause more pain.
"Dam flying rats" Jason mumbled as a heard of pigeons took off right above them as they turned a corner towards the Bat Burger, which was now in sight. Danny had to hide his excitement about not having to fight his food before getting to enjoy it. "Mother used to take care of a room of pigeons in order for Ra's to be able to send messages to those who thought cell phones made you turn green and go insane."
Jason, to his credit, didn't stop walking or change his pace, but he did turn his head to stare at who he thought was his brother who just randomly said something completely insane. He processed what he thought was a truth that came from his brother who wouldn't bother telling a lie. "Theres's people who think cell phones drive you insane and turn you green?" is what he asked once he could speak again. Danny had great control over his face, but it was still a challenge to not burst out laughing there and then. "Of course there are" Danny wondered if Damian would count this as 2 lies or just 1.
Danny got a delicious burger and fries; Jason got an unholy amount of chicken nuggets that he somehow managed to eat all of them within an hour. Day 4 was the only day Danny spent alone with Jason, which Danny thought was pretty sad and had hope that after it was revealed that he wasn't his twin he and Jason could kill some people together as the only 2 who seemed to not bat an eye at breaking dear Brucie's rules. It would also be nice to actually be able to float again instead of having to walk. Danny did miss being able to play video games while floating upside down. Days 5, 6, and 7 were bland and honestly, Danny was running out of ideas that could maybe be believed and wouldn't be something that they knew was false. It was on day 8 out of his 14 days long stay in the manor that he was alone with Barbara in the bat cave.
"So," she said after blatantly ignoring Tim on coms, making a very bad pun. "What do you think Damian wanted to do so badly to finally ask you to come here, and who's idea was it for you two to switch places?" Danny burst out laughing.
"Finally!" He yelled, "It's like none of them are aware of their surroundings at all!" Barbara was also laughing when Danny shifted into his ghost form and floated up a little before answering her questions, "Oh, it feels so nice to be in the air again" he took her lack of surprise as a sign that she knew absolutely everything about him already. "Dami wanted to go on a road trip without getting stalked the entire way, which makes so much more sense after spending a week with you guys"
Barbara smirked, "I know exactly where he is right now, like I'd let someone show up pretending to be him and not go looking" "It was also his idea," Danny was upside down now, "We're gonna tell them when he gets back and shame them all" "As you should, I'm also going to shame them, just because you two look alike you're not the same person" "So I also am guessing that you know about our bet?" When she nodded back at him, he continued, "I'm so out of ideas for them! You have any ideas?"
"What if you tell them that Bruce listens to K-pop in his free time? I'll back you up on it too" Danny grinned at her, "That's amazing, and if you back it up, they'll totally believe it no questions asked. You and my sister would be like, best friends. She is also 100% stalking where I am right now, but that's mostly because she doesn't trust the GIW to stay out of Gotham since I've come here" Barbara sighed, "That horrible branch of the government has been a personal project of mine to try to dismantle from the inside and not start an interdenominational war, but after finding out who the feared Ghost King is I could probably move a whole lot faster"
"Yay! I'm so sick of those guys following me around constantly" Danny was back on the ground now, "It felt so nice to be weightless again, it's so relaxing" Barbara smiled at him.
It was the next day when Jason, Tim, Barbara, and Danny were in the kitchen getting a quick lunch when the topic of music had been brought up by Tim, who was trying to guess what kind of music Jason listened to. He'd guessed a bunch of genres that honestly did seem to fit with what Danny knew of Jason. "Perhaps Korean pop, like father"
"Theres no way Bruce listens to K-pop, right?" He turned towards Barbara, who was eating her sandwich, seeming to ignore the conversation, Danny knew she was trying not to laugh though, "Of course he does Tim, there were even a few articles about it a while ago when it was mentioned at a gala" The two boys seemed only a little stunned at this point. With Barbara's help Danny was able to get the Wayne family to believe a grand total of 9 lies over the 2 weeks Damian was gone without being found out by anyone other than her.
When Damian walked into the game room where Danny was playing Mario Kart against Tim, everyone turned to stare at him and Danny. "How many did they believe?" Damian asked Danny. "9" Danny said, letting himself burst into a giant grin, Barbara mimicked that grin. That did seem to let everyone know that who they had thought was Damian playing video games with Tim was actually someone else and none of them had known. "How could you believe such blatant lies that could have been easily fact checked" Damian asked his family as Danny was having a laughing fit on the floor.
"I for one, am disappointed in all of you guys" Barbara spoke up, "Over the last 2 weeks Damian hasn't been in Gotham at all, and Danny has been in his place and also trying to see how many blatant lies he could get you to believe" Bruce hadn't said a word, his eyes going between Damian and Danny.
"Wait, who are you?" Jason pointed at Danny, who had recovered from his burst of laughter. "I'm Danny, Damian's twin" Danny took so much pleasure in everyone's shocked faces, "Where have you been living?" Bruce asked, clearly mentally preparing to adopt him then and there. "Oh, cool your adoption craving dear Brucie" Danny once again made Bruce blue screen, especially since he was here in the same voice that he heard from his youngest who was always the most formal no matter the setting.
"I have a great loving family that I was adopted by before I even knew who our grandfather was. The whole reason I made up so much stuff while I was here was because Dami promised me and my sister Jazz that for each thing you all believed he'd spend a day with us in Amity Park" Bruce seemed a little sad at this information, "Danyal also assured me that he would stay here for the next week to actually form a bond with our father while not impersonating me"
Danny and Damian had planned for Danny to start to slowly freak everyone else out with his ghost abilities. But that first night Tim brought up the topic of how Danny was able to be Robin so easily as he hadn't grown up with the League nor went through Bruce's crazy training, "Oh, I became a superhero before he did so I have a leg up on him"
"Who are you? I don't know anything about Amity Park enough to guess your 'hero' name" Time said, "Oh I'm Phantom," he said, letting his eyes glow a bright unnatural green that made Tim jump back away from him as he had only that kind of green with the Lazarus pits. "And don't worry, next to no one in this realm knows about me"
Phantom didn't join the bats for their night out for that week, mostly out of fear that it would draw the GIW to Gotham and he really didn't want to do that. So, he grew closer to Barbara and helped give ideas on ways that they could take the GIW down now that she knew that she could have the help of a ghost or 2 doing some stuff in Amity Park if it was needed.
There was a night where Danny heard Jason in the kitchen at a ridiculous time in the morning and decided to scare him by walking into the kitchen on the ceiling with his eyes glowing as brightly as he could make them while in his ghost form, and saying something in ghost speak, which meant that Jason was properly freaked out when he rubbed his eyes and the next second Danny was standing in the doorway looking normal giving Jason a confused look "I said, what are you doing eating cereal at 2 in the morning?"
When it was eventually time for Danny to head home again, he turned into his ghost form, and made a portal right into his room, "Dami, you better follow through on coming here for a week at some point, and I'll definitely visit again, maybe once the GIW aren't trying to tear me apart atom by atom and the law stating I'm not sentient is reversed" and with that Danny vanished into the portal.
The last thing he heard from his brother's family was "Excuse me, what the actual fuck?" From a bewildered Tim and a "Danny being here was certainly an experience" Barbara patted Tim on the back, before he was back in his room realizing that he had to fight his food during dinner tonight.