Using existing game titles, put them together to make your own title. Words like Mario can only be used once (unless you want to repeat it for comedic value).
For example, Mario Golf: Toadstool Tour + Mario Kart: Double Dash= Mario Golf: Double Dash, Mario Kart: Toadstool Tour, Mario Golf: Toadstool Dash, and Mario Kart: Double Tour.
You don't have to list all possibilities (or use just Mario games) like I just did, though. That was just the sample. :)
Anyway, here is one that I just thought of..
Super Mario Brothers + Dr Mario= Dr Mario Brothers, or Super Dr Brothers