Since I don't have 10 years of experience coding, for now I'm looking for pre-made code, as I'm afraid I can make a serious mistakes that I may not notice, or very inefficient code, etc.. Usually I can write code pretty well, but when I'm done and I look at the example, my code is either half of it ...

Love is what one could call a "library", not a game engine. That being said, i believe Love matches your requirements: uses Lua (a super simple and intuitive programming language), it's cross platform (windows, OSX, linux), handles 2D graphics, has an implementation of Box2D physics engin...

I want to develop a game that visually and somewhat physically looks like Mario or Megaman, etc.. I have average knowledge of C++ and have created a few simple programs. I like the sophistication offered in the language. I've noticed that Box2D is used for physics, however what else 2D-side-scroller...