What team do you use for the Clan Boss?

This quest is pretty easy for the straightforward clan boss team that puts the usual Decrease Atk, Decrease Def, Weaken, and Poisons. Just a couple rounds and it should be done.

However, this is relatively harder if you have a debuff extender in your team like Vizier, as you can't add more debuffs if the debuff slot has been maxed out. If this is the case you just have to use your other keys (maybe on other difficulties) just to add to the count for the quest. I've had this issue before and that's just what I did.

I have Elhain, WarPriest, Shaman and Trunda at the moment.  Could you please suggest another team? I have the below champions..

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Putting a multi hitter champ with toxic set could help if you struggle with that mission. Could also put it on a rare so that mission is complete when needed :)

Clan Boss teams are composed of 5 champions. Using only 4 champions is much less effective.

You may want to farm the Campaign for some very useful champions - Deadlands (Warmaiden drops there) and Durham Forest (Spirithost drops there). As farmables, they are pretty easy to get and to fully book.

You should also consider using your Pain Keeper. She is one of the best Rares in the game.

Get your Athel to level 50 and then to *6 / level 60. She will be of great use to you everywhere. She is a great Campaign farmer (in my opinion better than Elhain), and she will help you in Fire Knight and in Spider a lot too. She may actually be of use in early Clan Boss as well, as she has Weaken on her 3-hit A1.

You have Ghrush the Mangler. He has a high rating for Clan Boss.

Get as many Mystery shards (green ones) as you can. You will eventually get some ncie Rares. If you get an Armiger or an Outlaw Monk (both Uncommon champions), keep them. Use duplicates to book them (do NOT waste any books on them). They are extremely easy to Ascend, as they only need the small potions.

also keep in mind the ability to land debuffs will benefit greatly from a high accuracy and if you can land a couple debuffs each round (poison as just one example), then its a matter of being able to go 20 rounds or  more with the big guy