The team I said was:
1st - Tayrel -------------> Atk Down
2nd - Rhazin ------------> Def Down + Weaken
3rd - Frozen Banshee --> Poison Sen. + Poison
4th - Skullcrusher ------> Counter Attack
5th - 2 Different Options
A - Aox ---------------> Debuff Extension + Heals
B - Doompriest -------> Cleasening + Heals
If you add Ninja, he could only replace 2nd Spot or 5th Spot
If he replaces 2nd Spot, The team will miss out on Weaken Debuff.
If he replaces 5th Spot, The team will miss out on Consistency.
In Addition, I believe Ninja on a Skullcrusher team isn't good.
Ninja gains turn meter on the A1.
Ninja will get throw out of rotation.
In regard to Iron Brago, Iron Brago does Attack Down on a Cool Down move (A3 move).
Iron Brago Atk Down is for 2 turns on a 3 turn Cool Down Cycle.
Tayrel Atk Down is on Default move (A1 move).
Tayrel A1 move is double hit with each hit having a chance to trigger Atk Down.
--> Increase Defense Buff is a luxury skill
Increase Def Buff is very good to have in CB, but not at the expense of Atk Down
---------------------
In Summation,
I see no valid reason for Ninja to be on the team.
Every CB team scenerio I go over in my head makes him a liability.
I do see Iron Brago with a small hope of entering the team.
It would require a very specific set up to work.
In order for Iron Brago to be on the team, The OP would need to select Aox as 5th hero or another Debuff Extension hero.
Than they could replace Tayrel with Iron Brago.
Iron Brago Atk Down isn't consistent as Tayrel Atk Down, BUT if the OP knows he will have Debuff Extender on the team, He could take a risk and use the Debuff Extender to maintain Atk Down.
In the set up I gave to the OP, I didn't select a 5th hero.
I gave the OP 2 possible options for the 5th slot.
If the OP selects Aox as the 5th hero, Iron Brago could replace Tayrel.
If the OP selects Doompriest as the 5th hero, Tayrel should stay on the team