I do not know how much you already know, but it seems you've got the mechanics. So I am sorry if I write anything which is not new to you. I do not know all of your shown champs. Here are some of my thoughts.

These debuffs you need: ATK down, DEF down, Weaken, Poison and perhaps HP burn. 

Buffs: a 60% DEF on all allies would be good, Heal over time, if lifesteal do not procs, Debuff protection

Think about the masteries: do not set any turn meter skill. Set WM or GS (more than 2 hits on A1) in T6 of the masteries.

Try to get DEF of all champs above 3K.

Get all champs between 171 and 189 speed.

You definately need a champ which can apply ATK down during the whole clanboss fight. Coffin Smasher should work. Speed: faster than Valk, slower than cleanser (if needed).

Valk is probably the best counter in the game. Congratulations! She must go last, so she needs 171 speed at least, but definately less than all others. 60% DEF up would buff her shield.

Imho Stag Knight won't fit into a counter team because of his A1. 

Frozen Banshee as a poisoner seems to work fantastic. Do not know if a second poisoner makes sense, probably yes. But think about applying ATK down all the time.

You could try Spider for applying 60% DEF down and Weaken (only small version, 15%). Do not know his other attacks.

You probably need a cleanser to get rid of the stun, or you have a high resistance/DEF and low hp champ (as a tank), so that the stun cannot be applied. A cleanser must go first, so highest speed, max. 189.

Coffinsmasher great for CA CB team

With Valk CA you may not need a 2nd poisoner

Grizz Jarl is an interesting option for you

Honestly, you have Valk, and she's enough to carry your team.

Here's what I'd go with:

Valk - Counter-Attack, Shield

Frozen Banshee - Poison, Poison Sensitivity

Grizzled Jarl - ATK down, DEF up

Stag Knight - ATK down, DEF down (ridiculously high multipliers on his A1 as well)

The critical piece you're missing is Leech. I don't see any on your roster, but if you have one, that should be the last piece. You're also missing Weaken, but you don't really have anyone good for that yet. When you get Rhazin, you'll probably want him in place of Stag Knight, although you'll be facing an enemy without ATK down for at least one turn, which is risky.

rugnor goldgleam fills out both those niches and is generally considered excellent for cb. you won't really be able to speed tune him because of his kit, but it won't affect the rest of your team.

Yup Rugnor would do it. Didn't notice him in the champ list. Probably would want to disable his A2 in custom AI though.

Good call!.  And like Kram said disable the A2, so maybe:

FB (posion)

Coffinsmasher (atk down / hp burn)

Rugnor (dec def weaken)

Valk (CA shield)

Jarl (inc def / block debuff) -- Be optimal I think to A3 before the stun and have valk put up shield with defense up.  At least I think.  So would need to survive first few rounds naked so to speak

Why Coffinsmasher instead of Stag Knight? Seems like Stag Knight is just all-around better?

Coffinsmasher with ATK down on A1 (also a 3 hitter for GS) will keep it up 100% (not guaranteed but better than SK).  I would even consider disabling the HP burn skill and having CS just do all A1.  With Rugnor, Stag brings nothing additional to the table.  Stag is fabulous in dungeons and DT, better to be geared faster and stronger for that content imo.  

Stag + Jarl should be able to keep ATK down active the whole time, and Stag hits way harder than Coffin Smasher does IMO. Though Coffin is, admittedly, HP based, and so may be easier to gear for CB.

As always, thank you guys! Trips and krama you guys are legendary, always giving some great advice.

After reading all this, i think i might start with stag knight (Since he's already maxed out and geared for CB). ameanwhile, i'll work on coffinsmasher and maybe see if i'm still not managing with Stag, get Coffin in (and maybe even try disabling the HP Burn if i'm not able to keep ATK down all the time.)

So FB, Jarl, Rugnor, Valk, Stag Knight/Coffin Smasher it is! Will let you know how this works out. Also, do you think i would still need life steal gear? or would the leech with procs be good enough?

Cheers guys! 

Leech is more than enough, provided *all* of your champs are running Warmaster or Giantslayer.

I would build GJ with no accuracy to avoid the heal reduction from taking a debuff spot.  You need to be very careful with filling the debuff bar when using FB.  She will attempt A3 even when bar is full.  So disabling CS HP burn (and getting 3 hits on A1 everytime) and building GJ all Def/HP/CR/CD (no ACC) would be optimal.  But GJ is very good elsewhere, so as an early game player you likely will build more well rounded.

Hey guys! Just wanted thank you all for the suggetions! Finally got my team ready and clearing NM in 4 keys.

The funny part? Just when i got the new team ready, i did a few ancient shard summons and got extremely lucky, and seems like ive got some champions who seem like they could be useful.  Listing them below:

1. Iron Brago

2. Sepulcher sentinel

3. Captain Temila

4. Giscard the Sigiled

5. Tarshon

6. Occult Brawler

7. Gravechill killer

What do you guys think? I'm currently using Grizzled Jarl, Frozen Banshee, Coffin Smasher, Valkyrie, Rugnor Goldgleam.

Also, off topic, but which of these new champs do you think would be useful for spider?

TIA!

Iron  Brago  would  be  a  HUGE  improvement  over  Coffin  Smasher.  The  defense  from  his  passive  is  huge  and  he  brings  permanent  defense  up  and  attack  down.

Sepulcher  Sentinel  might  also  be  a  good  replacement  for  Grizzled  Jarl.

I  like  Giscard  to  replace  Coffin  Smasher.

I  didn't see  a  Spider  team  for  you.

You  would have  to  lvl  up  2  copies  of  the  disgusting  green  hero  named  Armiger.

I'm  completely against  it  though.

My  recommendation is  to  whale  harder  on  void  shards.

Than  complain  to  support  if  you  don't  pull  2x  ColdHeart.

It  is  the  only  valid  strategy.