Es bueno que la novia de Mario viene con nosotros.

I am really surprised that the condition here doesn't trigger the subjunctive: "Es bueno que la novia de Mario venga con nosotros." To note also that this statement is in reference to a future event.

I am guessing that either form is correct (subjuntive versus standard) depending on the mood you want to project. This sentence seems to be making an observation "It is good that Mario's girlfriend comes with us" versus a hope "I hope that Mario's girlfriend comes with us".