Can any other type combo cause all moves to be neutral, like ghost-dark?

Question

It can be a type combo not made yet.

Answer 1

No, aside from an electric type with levitate, like eelektross, or a poison-dark type with levitate, which doesn't exist.

Answer 2

Just look at the Dual Type Chart, on the right hand margin, where it tells the dual types with the most and least weaknesses. It's very handy!