My guy. I see you haven't quit, welcome back. I must ask you to take the time to read replies:
We need more information, like seeing your gear, other options for champions, where you're losing your champ(s), etc. That said, I think this might not be the wisest use of your energy at this time. Getting your best champions to 60 and getting your gearing in a better spot seems a much better use of your time and energy. This specific level can be quite annoying without some specific champions/gearing, too. You might be better off waiting until you can just 3 star it straight away, for energy efficiency.
I know you've had problems posting pictures of your roster/gearing, but if you do so taking screenshots from a computer while using Plarium Play there shouldn't be too much of an issue.
This entire thread is silly. OP, you are nowhere close to being in a position to be wasting time on trying to get stars in Nightmare campaign. There are very specific champs that can do it properly; anything else is just pointless. And, needless to say, doing it without level 60 champs is an even bigger waste of time.
Literally all you should be doing, is leveling food in Brutal 12-3, until you get a full set of champs that can farm Dragon 20 propery. Then, you should do nothing else but farm Dragon 20 until you have proper gear for your champs. Once that's done, you should get a Clan Boss team together that can get top chest on Nightmare.
Once *all* of that is done, you can consider possibly doing Nightmare campaign for stars.
I only play on iphone. Difficult to cut screen shots to fit. Perception and Life and Speed Gear mostly.
The stats a starter champ like Kael needs to do 12-3 brutal (not nightmare, brutal!) are really low. You can basically achieve that with the gear you got as reward from finishing campaign.
Below 100% crit chance, low crit damage - but it's enough to do 12-3 brutal and level up other champs as food. I'm sure your Kael has even better stats.
Kael + 3 uncommen champs that are supposed to be sacrificed as food in the tavern. Do that or start a new complaining thread in the forum every day.