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So im trying to build a competitive list at 1850 pts.
I was thinking taking as an hq choice\ immotekh or zandrekh and obyron what do you think? As troops los of warriors, some anihilation barges, ghost arks for the warriors, lychguard maybe, wraiths im pretty lost here...

Okay then, so what models do you have, or is there no limit?

So based on what you have said above, this is what I think you should take:

HQ:
Zandrekh and Obryon
Great choice in the current meta, most competitive lists have ways to buff and debuff units, this is one of the only way necrons can do this, but it is one of the best ways in the game. Psychic powers can be stopped, but Zandrekhs special rules can't be. Some of the rules he can give mean that some units can be given a new role every turn, e.g. tank hunting (tank hunters) and objective camping in ruins (stealth). But the best point about Zandrekh is that he can remove these special rules as well from an enemy unit, the best one is removing hit and run from a Deathstar. While Obryon is beast in combat, vs the right units. Also his in built veil of darkness is helpful, for quick movement and grabbing/contesting objectives late game. Also by taking both, you'll still have a spare HQ slot, for a destroyer lord maybe.

Troops:
5 warriors, or 5 immortals in night scythes
Best option, troops both stay safe and have good manoverability, for late game objective grabbing/contesting, obviously immortals are a bit more durable. Don't worry about backfield objectives because at least 1 night scythe will get destroyed at 1850pts and its troops will have to walk on, I know from experience. There's no point going above minimum squad size because your mostly just going to be dropping them off on objectives.

Elites:
5-10 deathmarks with a cryptek harbringer of despair
Nothing really stands out in the elites section, apart from maybe this unit. Great against deathstars and maybe a wraithknight. Maybe put Obryon here, if not take a night scythe transport.

Fast attack:
Canoptek wraiths and lots of them
Still one of the best units in the game by far. Take these in units of 5 or 6. Use Zandrekh's phased reserves to deep strike them in during the enemies turn 2 when they bring in at least one unit from reserves, if you use this tactic don't attatched any characters to the wraith units and always choose to go second.

Heavy support:
Annihilation barges
Cheap, durable and powerful, what more can you ask for.
3 canoptek spyders one with a gloom prism
These only work with Zandrekh, Obyron and destroyer lord. Creating a T6 Deathstar, 3 monstrous creatures, every model has 3 wounds and all 3 characters have a 2+ armour save to tank wounds. The whole unit can teleport and can be buffed up by Zandrekh.

Hope this helps, post up a list and I'll have a look through it.

Minimanj has the right ideas let me abbreviate them for you

Anni barge-bring 3 there only 90 flippin points! These are auto include IMO because of their points efficiency

after the barges your list should go one of two ways;
wraith spam( atleast two units of 5-6 like minimanj said) If you go with wraiths i highly suggest bringin Destroyer lords as they confer preffered enemy to their unit (attached to wraiths) they can also move 12 right along side the wraiths. in this case with the wraiths being strength 6 almost always wounding on a 2 or 3 in CC re-rolling ones means lots-o-wounds.
Wraith builds tend to benefit from slim troops in nightscythes (atleast 3)

The other direction i would suggest which IMO is just as dirty would be multiple ghost arks. Atleast 3-4 however in this case you should be going troop heavy (9-10 warriors in each). Zahndrekh works better in this list as he can ride around in his armour 13 whip and draw line of sight for his special rules anywhere from the hull(ghost arks being open topped)
so there it is Wraith heavy or Ghost ark heavy you decide either can be supplemented as you choose. Both work well in competitive enviroments