Supersquig, you're in luck, because the list doesn't look ultra cheesy. I think we can mix something up for you 8Y.
Against Nids, you'll need 2 main types of weapons: Long range shots with a high strength & low ap & a whole lot of basic fire or heavy bolter rounds. These two ingredients are the way to deal with a pesky Nid infestations.
If you're custom-building an army strictly for countering Nids, then might I suggest the following:
HQ:
Chaos Sorcerer w/ Flight & Lash of Submission
*Works on Monstrous Creatures as well, but most importantly, it delays the swarm rush by 1-2 rounds.
ELITES:
Chosen w/ plasma guns
*The plasma gun is a user-friendly weapon against Nids, as it shoots high strength, mid-ranged shots for dealing with monstrous creatures, and then you can double tap it when the swarm draws near or to finish of an encroaching Hive Tyrant.
TROOPS (the more the merrier):
Chaos Marines- 10 man squads with dual plasmas & a champion with fist
*Don't be tempted by our numerous icons. Leave them be, and simply equip each marine squad with the Glory Icon. Against Nids, you need all the basic bolter shots you can afford. Take dual plasma guns, as well as a fisted champion for contending against any residual monstrous creatures that survived the march to your side of the table. The champion with a fist is optional, as he's rather expensive; however, I've found him to be immensely useful for clean up duty.
Noise Marines: Two configurations
8x noise marines with 7x sonic blasters & a blastmaster
5x noise marines with 4x sonic blasters & a blastmaster
*Both units work well, as they're obviously very destructive against the swarm. I prefer three 5 man squads over two 8 men, as they're comparable in price and yield an additional blastmaster. If your build includes a sufficient number of plasma guns and missile launchers, then you can sometimes get away without equipping blastmasters in your noise squads.
HEAVY:
Havocs: Two configurations
8x havocs with 4x missile launchers
8x havocs with 4x heavy bolters
*Your basic essentials for managing Nids. Missiles for the big beasts, and heavy bolter plugs for the little critters.
For a more versatile build, you should consider the use of vehicles. However, against Nids, our basic bolters are just incredible, which is why I suggest fielding units that have sufficient basic fire.
