Biovores and stranglethorn/barbed strangler don't exactly work well against warriors in cover. It won't kill enough quickly enough for it to matter if the Necron player has a lord w/ Resi orb and a ghost ark.
Then again, I may just suck at rolling. I have terrible luck against cover as Nids.
That's the thing. The right list won't worry about the cover. Necrons have limited range. So, you build lists around exploiting this. You have three possible win conditions. Two of which are objective.
Harpy with venom cannons and tyrannofex's to go for the vehicles at range. Biovores and warriors with stranglehorn to take potshots at range. Unless the Necron player is using Phaeron, he can't move and shoot worth a damn. So, let him sit in cover. Who cares. The goal isn't to kill, it is to win. Priority targets are doomsday barges. Once they are gone, heavy destroyers and any other range 36 weapons.
Punish the player for using cover. Exploit the weaknesses. Got scarabs, blast templates.
Got wraiths, shoot them with hive guard.
Hit the monolith with MCs.
Shoot the annihilation barge with range 48/36 anti-tank.
Every vehicle is open top.
Stay outside of the range and make him move.
Play the objectives.
In killpoints, take out the vehicles.
In objectives, camp them.
Nids have guns, use them.
With Grey Knights, Dark Eldar, Guard, and now Necrons, if we play the mindless beast, we get pawned.
Control the board and control the movement. It works.
Here is my current all comers, and it has been working.
Hive Guard 3
Hive Guard 3
This is about 2000pts.
The basic idea is don't play their game. They want you to charge. Currently, Nids are at a disadvantage if they do. When move through cover gives us assault grenades, then things will be different, but for now, we got to suck it up.
You have 4 48 inch shots that will do beautiful things to open-topped AV 13.
You have 3 48 inch large blast templates that cause pinning.
You have one 36 inch blast that can pop an AV 13 if you are lucky or instant kill destroyers, wraiths, scarabs, etc
Let them come to you. They move, they don't shot 24 inches.
At 24 inches, you have 12 st 8 shots that you don't need LOS for. Abuse that.
At 24 inches you have 2 AP3 blasts.
At 18 inches you have 2 large blast.
At 18 inches you have 60 shots that if the unit shot at has to take a leadership test, it does so at -1.
And you make your own cover.