I am developing a game, and since I haven't decided on a name yet, I've named it say, Project Deadpool. I plan to release the game as a beta. Will this cause any problems. It is just a name until a proper name can be decided.
Imagine your game attracts the attention of Marvel or any other company's lawyer sometime in the future. For whatever reason, sound or unsound, they claim your game is infringing on their intellectual property and tell you to take it offline.
If you go to court to argue that you didn't use any of their IP, and they present evidence showing the original name of the project was literally the name of one of their properties, that doesn't help your case. To a neutral observer it may look very much like you set out to deliberately infringe on their IP, later name changes and other differences notwithstanding. You'd have to work that much harder to change a judge's mind in your favour.
So why put yourself in that position in the first place?
Generally it's better to avoid getting into such a situation from the start. Getting into a legal battle with a huge company can be astronomically expensive, whether or not you've broken any law. The economics and systems of IP law tend to encourage these companies to be very protective of their properties, so the general not-legal-advice recommendation is don't go out of your way to bait them. ;)