How to beat necrons?

I have a tendency to complain about how overpowered I think Necrons are, and I have one Necron I think is cool and don’t complain about: Nemesor Zahndrekh. I made a joke about him being the best, and now my opponent is playing a match against me using him to prove my hypocrisy.

I don’t know how to counter Necrons and would like help.(legends are allowed)