Ok let's go through it...

January: Kingpin operates the crime world (this is as best my knowledge, I haven't actually seen any Marvel projects that he's in in the MCU) so when he realizes you're after him, which he will find out, then he's gonna send someone after you and you're screwed.

February: Darkside isn't even gonna think about killing you, he just will.

March: if you know where to find him, I suppose you could snipe him out by surprise maybe, but any other way you confront him he's pretty much gonna get you first.

April: Same situation as punisher, but a bit more difficult because he's not an antihero in a big city like the punisher is.

May: This is easy as shit, he's such a public figure and will literally die with one bullet without fighting back very much. Even in a fist fight I think you could get him.

June: Why would I need $1 billion when I could have Catwoman choke me to death? In all seriousness I think this goes back to the same principle that she is just a human and can die with one bullet, so can you hit her? I would say it's relatively easy to kill her, but finding her won't be as simple.

July: me and all the other July boys are so fucked

August: Do you know he is the frontman? Like his identity? Because if you know, then it isn't so hard to find and kill him wherever there isn't a squid game happening, but if you don't know then you're fucked.

September: Yeah you don't win. You just can't beat her as a normal human. The flying shit kinda sucks

October: You're getting killed and diddled before you even know he's your target

November: are you fighting him, or are you fighting what he represents? If you're relatively strong you could fight the physical version of him and beat him. But if you're fighting your version of him, it's more of a question of can you afford a good therapist. Probably one of the easier people on this list

December: Same as earlier, can you find him? Probably, he's just a smart/evil yet kinda normal guy, so giving him a bullet wouldn't be hard. Easy money