Make it illegal for war criminals or people with ICC warrant to enter NYC

Most (all?) criminal laws are written at the state level, not the city level. For example, NYC probably doesn’t get to define what constitutes an assault, burglary, or theft within the city limits. With out-of-state warrants, usually there’s a state law that allows police to (for example) arrest someone in New York for a Virginia warrant, then look at extraditing them to Virginia. I doubt it’s that clean for international warrants, as U.S. states probably don’t presume any international warrant is legitimate the same way they presume warrants from other U.S. states are legitimate.

Maybe there are carve outs in some cities that allow police to arrest people for violations of certain city ordinances, but a lot of minor stuff people get arrested for – disturbing the peace, driving without a license – are state crimes. If there is some New York law allowing NYC to create local ordinances and allow arrests based on violations, I’d be surprised if it’s just blanket power to effectively create any criminal law you want (such as making it illegal for someone with an ICC warrant to enter the city).