So, I have been already reading over the codex some and some nasty works have already started to surface.
Take a few Crypteks to lead your Warriors or Immortals. Notice I left Lycheguard and Deathmarks out, that is because they are both elites and there is better choices to be found among elites.
Give all Crypteks the Harbringer of Destruction and give them all eldrich lances. This will give each Necron unit a 36", STR 8, AP 2 move and fire lascannon. This is huge to soften up mech armies before the entire army is in range to rapid fire them to death.
Second the Solar Pulse is a must have, take 2 or 3 if you can afford it. Why? Because you can either cancel night fight or cause night fight. You can even engage it on your opponents turn. So, they have first turn and a nasty Alpha Strike army? *lights out* Oh you can't shoot? Damm....do this multiple time and watch an IG player go bonkers that is used to sitting back and shooting down his targets.
Orikan the Diviner plus C'tan with Writhing Worldscape and Grand Illusion:
The package here is another nasty surprise, while it is an investment it can work to be an ugly one.
Orikan's Temporal Snares: During the first game turn, all enemy units that move count as moving through difficult terrain. If they are actually moving through difficult terrain, then a unit must move and take the lowest d6 result on their test.
Writhing Worldscape: While the C'tan is on the field all difficult terrain is also dangerous for the enemy. If the terrain is dangerous, they fail on a 1 or 2.
Grand Illusion: After all deployment and scout moves, you may redeploy d3 enemy units subject to normal deployment rules. You may even take models out of reserve or put them into reserve!
The dinner table now: So, you have here is all enemy units count as moving through difficult terrain first turn. If they are already in difficult terrain they take a check on two dice and must take the lowest. With the C'tan now all difficult terrain is dangerous now. If the terrain is dangerous they fail on a 1 or 2. So, now all units are rolling two dice for difficult terrain checks AND are forced to roll dangerous terrain for each model. Grand Illusion can either put models into cover (if they are are jump troops for example) to force difficult terrain checks or you can move them out for units that rely on terrain for cover like IG. In any case, you can manipulate the battlefield to a serious control situation. Either they will take the risk of losses or be afraid to move as they are worried of the end results.
Add some CryptTeks with Tremorstaves instead of the Solar Pulses if you wish to maintain this pressure for each turn.