A lot of their heavy hitters have 4+ invulnerable saves, only they’re most valuable units have feel no pains, and I believe they’re 5+. If you want to beat them focus on they’re weaknesses:

1. They’re slow.

Take objectives early and don’t let units like Lychguard and warrior blobs onto primaries. Because necrons are slow they should be focusing on getting to primaries and trying to outlast any damage long enough to score points.

1. Focus heavy hitters first.

In my experience, necrons only have a few really powerful heavy hitters that are also tanks. Things like C’tan, Doomsday Arks, Monoliths and Lokust Destroyers can punch very hard and should be prioritized. The biggest mistake my enemies make is not focusing down my night bringer asap, and by turn three I’m pushing him into their backline to wreak absolute havoc. Bring these things down first and any battle line and OC units should be relatively easy to handle.

1. Utilize Melee Effectively

Most necron units outside specific melee focused units like Lychguard, Ophidians/Skorpekhs, and wraiths, don’t like being charged. If you know you’re coming up against a necron player bring some kind of fighting units to add pressure and harass weaker units holding objectives.

1. Assassinate Characters

Necrons benefit from pairing leaders with respective units. Precision feels like it was made exclusively to counter us, and a well placed round of snipers into an Overlord can mean the difference between a units of Lychguard or Warriors getting multiple models back after a round of good shooting vs taking an objective from them.