If Mamdani needs an extremely unlikable billionaire who's using his vast unearned wealth to actively make the world a worse place, I have a suggestion.
Mamdani and his allies are tenant organizers, and their chief tactic is to identify specific villains.
This creates an illusion of accountability (as if the city's fiscal challenges can be assigned to some external bad actor rather than the cumulative impact of buck-passing), emotional engagement (find a focus for public anger and resentment that is not you), and polarization (if you don't join in the outpouring of hatred, you are suspect).
The trouble is that the villain needs to be a vulnerable target you can cut off from key resources (money, public support) through intimidating public protest, a media campaign, etc.
Mamdani has decided not to make Trump the villain, possibly because Trump has cards to play and doesn't seek the approval of Mamdani's base. Hochul can't be the villain, as the mayor is begging Albany for money. He decided to go after Ken Griffin as a stand-in for nonresident owners of expensive investment properties in NYC, but of course Griffin is not obliged to take the abuse. There's a good case that NYC needs Griffin more than Griffin needs NYC.
So who's next? Without a villain, it's not clear that the organizer's playbook can work.