I just tell you what I know. I do not play with your mentioned champs except Kael. Concerning cb you would mostly choose livesteal, so your champs do need no heal buff. T6 mastery on every cb champ is a must of course. As much life and DEF is also important. Speed must be high enough, too. Nightmare has approx. 180 speed if I am right. Imho at least counterattack buffers and other supporters should be at least slightly faster than the cb, so that they can cast their buffs regularly before cb attacks. CB champs should be fully "booked". Kael is still my cb champ with the highest dmg output (the other four are Foli, Scullcrusher, Steelskull and Tayrel). With ACC I am not sure how high it should be (do not know if plarium have said anything about that topic so far). With the Great Hall buff I have got ACC on debuff cb champs at least at 170. I think the higher your ACC is the better.

Do you have a screenshot of the heroes you own or can you write a list of the heroes you own?

Most of the Rare's I've seen recommended I don't have, but here's the list of potentials.  I certainly don't have a counter-attack option.  Currently Apoth, Draco and Jareg are my must haves, it's more those last two slots.  I've still working on maxing my masteries on everyone (actually, still wondering which one would be best for Draco?)

The 5 heroes I would use would be the following:

• Jareg
• Draco
• Apoth
• Aothar
• Flesh Tearer

The important thing will be making sure you get your move orders right

1st move: Apoth - Turn Meter + Speed Buff

2nd move: Jareg - Atk Down

3rd move: Draco - Def Down + Weaken

4th move: Aothar - 4x Poison

5th move: Flesh Tearer - Extend Debuffs

The second most important thing will be making sure you get the right debuffs to land on Clan Boss!

Draco + Aothar can do 8 poisons in 1 go.

You have to be extremely careful.

You want to make sure you have Atk Down + Def Down + Weaken on the Clan Boss before you do your crazy poison spam.

Otherwise, What will happen is you will have no room left on the Clan Boss to put them!

The Clan Boss can only have 10 Debuffs on him at 1 time.

So you have to make sure you can get the other stuff on before your poison heroes go wild!