‪ It would probably be something like if some big bad managed to capture Ivy and Joker both (probably among a couple other villains) my guess as to why they wouldn’t get Harley or Punchline is because they both managed to escape in time. Maybe they did it as a power move or to get access to their retrospective toxins or whatever. They wouldn’t team up more so as keep bumping into each other while investigating or something like that. Maybe battle once or twice, maybe not depending on how time sensitive the situation would be. Somewhere there would probably be a situation where they would both realize they needed to work together (idk exactly what it would be off the top of my head, honestly maybe just strength in numbers). Their fighting styles combined could have some really cool visuals. They’d both be irritated by each other but respect each other because they’d both be pretty good assets both intellectually and physically. I could see them nerding out a bit together over detective work as their figuring out things because they both have been shown to get really excited when they accomplish things. Harley also probably has rudimentary chemistry skills just from going through med school and being with Ivy for so long so I think she’d actually think Punchline was pretty cool if she got to watch her work up close AND she’d totally think her knife skills were cool in instances where they weren’t being used against her. I also don’t think it would end in them being friends by any means but Harley would probably say something along the lines of “ya know what, you’re actually pretty badass” or something because Harley does love strong smart ladies. ‬