…well what do you have, or do you proxy everything?
You can see a similar matchup at miniwargaming…
http://www.miniwargaming.com/content/orks-vs-necrons-waaagh-battle-report-part-16
…and as you can see…dont mass your points in a few models…
If he really fields that much of green meat, try the big guns (maybe all 3 of them)…i think theyre called doomsdayarks but im missing the english expression sry..
…Trazyn is also a weapon of mass destruction…hope that helps…and good hunting

lots of tesla and pie plates. definitely zahndrek, counter attack and furious charge will help you out. wouldn’t bother with trazyn, his empathic obliterator doesn’t work when he’s on his barge (stupid FAQ) and he still needs to kill one normally before he can try and set if off. throw in some ghost arks for the free ‘crons (well pretty much free ‘crons). if you really don’t like his big mek and grots unit then go death and despair combo (harbinger of despair in a deathmarks squad). 2 maybe even just 1 of those units should take care of them easily.