What @Captaniser has missed out here is that the Necrontyr were fighting amongst themselves and it was the plan of the Silent King to declare war upon the Old Ones to get all the warring Necrontyr Dynasties to unite against a common enemy, not just because the Necrontyr disliked them. This worked until the Old Ones began to win the war, and then the Necrontyr started to fight amongst themselves again. The C'Tan then proposed a deal that if they gave the Necrontyr new power beyond their previous understanding, the Necrontyr would help them to destroy the Old Ones. The Necrontyr accepted not knowing that they would be enslaved by the C'Tan as soon as they went under biotransferance. As soon as they became Necrons the Necrontyr then rebelled against the C'Tan and broke many of them into Shards and destroying one of them entirely (I forget his name), before retreating into their Tomb Worlds and beginning the Great Sleep. Even though I prefer the new Necron fluff, I don't see why there couldn't still be Necrons that are still under the command of the C'Tan and still remain loyal servants to them, perhaps the Necron Enslaved or a similar army like that, who hate the Necron Dynasties who mutinied against their masters and aspire to claim all the C'Tan shards and reform them into the original Star Gods. Just because someone at GW decides to change everything, doesn't mean that you need to follow them. I ignore the bollocks GW introduced in 8th Edition 40K about Hive Fleet Leviathan failing to devour Baal - I think the Tyranids would have slaughtered the pathetic Blood Angels, stripped their measly planet of biomass and sent the few survivors packing any day of the week, and as far as I am concerned, that is what happened - Tyranids win, Blood Angels lose. I still play Fantasy whenever I get a chance, regardless of any temptations towards AoS. Resist the darkness of GW's lore and make up your own! You could make an unofficial army book or something that's more similar to 3rd Edition Necrons and say that these Necrons are out to enforce the will of the NIGHTBRINGER!