The question is of Intellectual Property rights. (That's the term you'd use to look this stuff up.)
In short, anyone who owns anything can sue you for any reason. It is up to a judge to decide if it is a valid lawsuit/claim/etc.
So technically if I write a short story about taking a poop, I can then sue Activision for stealing my poop plot (intellectual property) for their Call of Dooty. Would I win? No. But the point I'm trying to make is the barrier of entry for a lawsuit is paying a lawyer to file paperwork.
With that in mind, most people/companies will not file lawsuits unless there is a chance they can win, they must do it to preserve their intellectual property, or if they want to harass you (that one is pretty rare when it comes to large companies.)
So what kind of IP lawsuits you will lose?
-Directly copying names/titles.
-Directly copying characters.
-Directly copying stories.
-Directly copying artwork.
What kind of lawsuits you would win?
-Copying Gameplay (IE rules, but not verbatim)
-Copying Level layout
-Copying broad plot themes.
So with your Robocop example. Do they call him Robocop? No. Does he look like 2d video game robocop? No.
Is Broforce a comedy? Yes. If they were to be sued, they'd win the case. Brobocop is not named Robocop. He not 100% copy of any official 2d sprite Robocops, and Broforce can always claim parody.
Please note, that most people who get caught in hot water with IPs are remaking games, like Pokemon or Metal Gear Solid or Dragonball Z. In such cases IP holders must sue or they risk losing rights to these IPs if someone were to challenge them. My advice for anyone who wants to make a Pokemon clone... Show a little bit of originality and change the freaken character names, title, and don't copy the artwork. Then you won't get C&D letters!
A good case study with this stuff is the "Unseens" mechs in FASA Battletech.
So TLDR summation on IP laws:
1) Anyone can sue you for any reason.
2) Do not copy names/titles
3) Do not copy story lines, character stories, etc verbatim.
4) Do not exactly copy artwork.
5) If you are close to violating any of these rules be sure you are not close to violating any of the others. A fat Italian plumber, with a red shirt named Marco, who saves princes is more risky than a "fat Italian plumber" or a character named "Marco" who "saves princesses. "
6) Everything else is fair game. (Gameplay, level layout, etc.)