Do you already have a campaign farmer that can farm Brutal 12-3 in 10 seconds or less? If not, Fellhound is a good choice for that, and will help you here too. Otherwise, don't aste time with him.

The rest of your demonspawn aren't worth spending resources on. Diabolist is okay, but I wouldn't waste the time. Just wait for better ones.

Oh I just pulled Infernal Baroness. Does this make any difference?

Also not worthwhile. Demonspawn Epic champs aren't really that amazing, and basically none of the Rare champs are worthwhile at all. Here's the ones I would level:

Demonspawn Epic Champion

1. Achak the Wendarin (DS-ESF)
2. Akoth the Seared (DS-EDM)
3. Alure (DS-EAM)
4. Duhr the Hungerer (DS-ESS)
5. Magnarr (DS-EHS)
6. Nazana (DS-EHF)
7. Peydma (DS-EDV)
8. Umbral Enchantress (DS-EDV)

Demonspawn Rare Champion

1. Diabolist (DS-RSM)
2. Fellhound (DS-RDV)

And the rare ones I probably wouldn't even bother with, unless you're really desperate.

I only have Kael for campaign farming and he takes about 16 seconds. So, perhaps I will develop and use fell hound. That will give me motivation to upgrade, gear and use fellhound and diabolist for faction war. and the ones I've been using. Thanks for the suggestion. :)

The reason I was thinking about Tarshon was one of his abilities have 60 % defence up and I was thinking it would hugely boost Ultimate death knight's damage output. He puts a lot of damage considering he also debuffs and protects his teammates.  

UDK is Undead Hordes. Tarshon is Demonspawn :)

That said - I think maybe Tarshon was buffed recently, because he's actually not bad. I don't love that his A3 has a 4-turn CD, but an AOE weaken is pretty good on the A2, and the A1 provoke is nice candy.

Oh, I was thinking I could use Tarshon in dungeons now and then, like when Kael suffers affinity problem. Everytime I decide to leave Kael behind, I get worried, but the second debuffer suddenly turns into a nuker when he stays out. Nevertheless, I realy need another nuker, not that I was thinking Tarshon would make a nuker, just thinking Ultimate Death Knight will deal more damage when Kael has to stay out.

Also, just realized that Kael takes much longer to finish a round if food champions do not all die in the first round. Last time, I checked it was 26 seconds.