Forum adverts like this one are shown to any user who is not logged in. Join us by filling out a tiny 3 field form and you will get your own, free, dakka user account which gives a good range of benefits to you: No adverts like this in the forums anymore. Times and dates in your local timezone. Full tracking of what you have read so you can skip to your first unread post, easily see what has changed since you last logged in, and easily see what is new at a glance. Email notifications for threads you want to watch closely. Being a part of the oldest wargaming community on the net. If you are already a member then feel free to login now.

HQ:
1x Cryptek /w solar staff, tachyon arrow

Troops:
-10x Warriors
-10x Warriors
-6x Immortals

Fast attack:
-9x Tomb Blades /w Nebuloscopes
-4x Wraiths /w whip coils
-4x Wraiths /w whip coils

Heavy Support:
-1xDoomsday Arc
-1xAnnihilation arc /w tesla cannon
-1xAnnihilation arc /w tesla cannon

Total: 1501

I recently decided to start playing WH40K again (I used to play 'nidz a lot before) and I decided to start a new army. I'll be mostly facing assault nid army and usual DE venom/ravager spam. I'm fairly clueless about what to do with my troop slots. Thank you for help.

You've almost got three formations there. With a bit of tweaking you'll have a decurion. You'll need to find a way to swap the cryptek for an overlord, and your second set of of wraiths for a spyder and some scarabs, but decurion is much better than a CAD.

Well, I did consider a spyder and some scarabs but is that formation really worth it? I'd be quite concerned with wraiths outpacing the spyder and losing the benefits. I'm also not that keen on scarabs as I'd struggle to find an use for them during games.

I'd go for a Decurion.
Besides the mandatory formation I'd add a Canoptek Harvest formation.
This would give you a decent 1500 pt list.

So, an updated list would look something like this:

Reclamation Legion:

Overlord /w solar staff
10x Warriors
10x Warriors
6x Immortals
9x Tomb Blades /w Nebuloscopes, shadowlooms

Canoptek Harvest:
-Spyder /w particle beamer, fabricator claw array
-5x Wraiths /w whip coils
-3x Scarabs

Annihilation Nexus:
-Doomsday Arc
-2x Annihilation barge /w tesla cannon

I agree with the updated list the Decurion is a much better option than a CAD