If you want nightmare, you need to get the suggested to 60.

Tayrel as leader

Occult brawler

Apothecary

G

Kael

I assume you mean Ghrush. 

Maus mage better than kael 

Can athel at 60 do the job? Im new player ..stuck on nightmare.grr.. ive got athel at 50 .. is harrier worth taking to 5 stars for this endevour too? Maybe hell last more than 3 rounds hehe.his attack is powerful though...  ive got corpse collector at 50 but my undead hoarde crypt isnt at level 7.. just sacred order crypt

For now i would use Lyssandra for speed boost, Tayrel for decrease atk/decrease def, Occult Brawler for poison, Sinesha for healing, and Zargala for weaken/decrease def. Lyssandra, Tayrel or Zargala in lead depending on which Aura you need most.

You will still be light on healing, so i would look at leveling/ranking up Ghrush the Mangler right away for leech/healing and then either Mauseleum Mage for stun block/healing or Bulwark for debuff extension or Kael for additional poison, replacing Lyssandra and Sinesha.

FYI, very important to focus on boosting def for your CB team, even if its not a primary stat for them, anything less than 3k def and it will be unlikely that you get past turn 20 with those champions that are lower.

I wouldnt bother with ranking Athel to 60. I dont know what the rest of your CB team is like, but from what youve mentioned that you have ready for ranking, id go with Corpse Collector. Leech is all you really need for healing once youve got all your CB champs Warmaster or Giantslayer masteries, and the extra poison from her A3 will help with damage as well.

Leader: Bulwark - Defense Aura

Tayrel ---------> Attack Down + Defense Down

Bulwark -------> Weaken + HP Burn + Debuff Extension

Occult B. ------> Poison

Apothecary ---> Speed Lapping + Spot Healing

Thenasil -------> Increase Defense + Team Healing

What ever u put make sure full mastiers 200 plus speed and 240 and up debuff resist or that wont work at all lol