Henchmen for Hire
AKA "Danny is employed as one of the Rogue's henchmen and he's doing so well at being discrete, none of the Bats even know he's committing crime! (They absolutely know.)" prompt idea!!
Y'know what would make this funnier?? Is if Selina Kyle, Catwoman and hoarder of strays, immediately Work Mom'd this kid.
Imagine Danny gets dumped into Gotham by himself. Except there's, like, no ectoplasm - not nearly enough to sustain his Ghost. So, his Ghost form slowly peters out and he's left penniless and powerless on the streets of Gotham. Obviously, the next step would be to find money. But how?? He can't go invisible, intangible, or Full Ghost to help him out here. And there aren't a lot of stand-up places that hire kids younger than 13, so ultimately he's forced to apply for henchmen positions. He doesn't actually find Catwoman's ad. No, she hears through the grapevine that this actual child is applying to be a drug runner for the Penguin or - oh, shit, the Joker??
Absolutely not. Selina is no saint, but she's not going to let another kid be beaten to death by the Joker. Maybe she talks to Harley and finds out where the kid's going, or maybe she just puts in an ad and hires him on the spot. To be honest, she doesn't really expect to particularly like the kid - she'll have him pick up her coffee or something, pay him at the end of the day (standard henchmen pay periods since it's likely they won't live through the end of the week), and clear her conscience.
Except Danny is a little shit.
Danny, for his part, doesn't necessarily want to be a henchman but he figured it'd be more than getting some lady's coffee, right? He imagined an evil man twirling his extra long mustache and smoking a cigar, or mobsters hunched over a gambling table grunting about... playing cards or something, he doesn't know. Instead Danny's told to pick up Catwoman's dry-cleaning. It's almost an insult when he knows she's planning a heist that includes stealing several very expensive items from a museum during an evening showing. Without him, her only henchman!! (So what if he snooped in her office? It's not like it's ghost-proof; she should've expected Bad Behavior from the Very Bad Criminal in her house.)
Selina finds out very quickly that Danny is akin to a rambunctious kitten chewing through her phone charger cable and clawing at her favorite muslin blanket (the one Bruce gifted her from one of their dates). And she's so exasperated that she agrees he can be involved. But only as a distraction and he's told that he needs to scram once the police come because she's not bailing him out of juvie if he gets caught. (She wouldn't, but she could make Bruce do it. Her lover would take one look at Danny's watery doe eyes and cave like he's already experiencing Empty Nest Syndrome.)
So, Catwoman and her littlest henchman plan to rob the Gotham Museum. She buys him a cat-themed facemask (in case things get sticky and he needs a quick anonymous getaway) like ones from Party City, it has little ears poking out from the top and it's adorable. And then it's go time.
Danny's role is to distract the crowd by pretending to be a lost kid and distract Batman if he shows up. Selina will take care of the rest - disarming the alarms, timing the museum workers' shifts, bribing the West Entry security guard, frame-freezing the surveillance cameras, smuggling in the forgery and smuggling out the original, and - well. It'll be nice not to deal with the Big Bat if he shows up, but Selina is used to doing this on her own.
She should've expected that Danny doesn't do what's expected.
Because Danny does his part as the crying, screaming child whose mother is lost amongst the chaos once the museum's power shuts off. He distracts the guards easily. Selina hides away the art, replaces the forgery on the wall, and goes to find her little stray. And Danny is clinging hysterically to The Batman, refusing to be pried off by security guards and museum workers. He's straight up sobbing. Talking about how he loves Batman and Robin, his family is dead, he wants to be Robin, did you know you should be able to see Ursa Major from Gotham but you can't because of the smog, do you think Poison Ivy can just make a lot of trees to unpolluted the air, Nightwing is his favorite superhero, do you think he'll sign an autograph-.
It's astounding how fast that kid can speak while also smearing green snot onto Batman's cape. Danny proves himself to be even more unexpected when he goes off-script, eyeing her and screaming, "Mom!" And Batman's eyes catch hers. Shit. How can she explain a tiny child calling her mother in front of her lover? That'll be an awkward conversation.
Catwoman doesn't take Danny to outings after that. Instead, she has Harley and Ivy take turns "babysitting" (i.e., using Danny as Batfam distractions) while she's at work, kind of like having the fun aunts take you shopping. Danny can do whatever he wants!! With the exception that he needs to be wearing his cat-mask at all times, to properly conceal his identity (neither woman knows he'd already thrown himself at Batman without his mask).
So, while Ivy is destroying a toxic power plant, Danny is stealing Nightwing's escrima sticks, clinging to him, "accidentally" tripping him, doing the Koala-leg thing. He goes all out when Nightwing actually does trip on him - he shrieks that he broke his arm, which forces the vigilante to pay attention to him. Sobs, clings harder, and endures the trip to the hospital on the back of Nightwing's motorcycle with a shit-eating grin.
Harley is beating the hell out of some of Joker's gang. Red Robin is doing surveillance and coordinating with GCPD so they can get the whole circus to Arkham. Except Danny is calling out where Red Robin is hiding with the glittery pink microphone that Harley bought him (originally to sing Doja Cat and Chappell Roan in her car). Joker gang's priority will always be the Batfam because of Joker's obsession with Batman and Danny uses the distraction so Harley can get a couple good swings of her bat in. He cackles maniacally when he hears a muffled, "C'mon, kid!!" from Red Robin.
And the Batkids are just like, Jesus, this kid is literally a nightmare. But they can't do anything! Are they going do arrest a kid? No. Are they going to arrest Batman's lover? No! So, they're stuck dealing with this.... absolute gremlin of a child!!
Danny, of course, is very pleased. The Bats have no idea who he is because of his little cat-mask, he's getting paid literally several grand per week, and Selina - who he's been living with ever since she realized he was homeless - even got him goldfish!
(Bruce is in his office, eyes crinkling in that iconic Dad-Smile, scrolling through candid photos Selina snuck of Danny's chocolate-smeared face while the kid was passed out on her couch. There's a fake ID under the name of Danny Fenton and several pages of foraged school records in a pile on his desk. Bruce eyes his desk drawer where several emergency adoption papers are tucked away.)
