For soul / traitstone farming I’ve been using:
Dragon Soul
Ragnagord ** (for Fast)
Acolyte *** x2 (for Necromancy and bonus Brown)
Plus the Brown +2 banner.
Ragnagord only needs 7 mana to fill, so with the +2 from the banner and +2 from the Acolytes one single brown match charges him up. Next turn he explodes, which usually fills Dragon Soul. Then just use TDS if charged, or Gord if not, until you’ve hit the 80 Soul cap (3 casts).
It’s not quite as speedy as other teams in Explore but it’s pretty close, and I’m clearing 150+ Souls per match (with the +100% soul armor I get 153 if everyone dies with 2 TDS casts, 180 if 3).
I tend to retreat if the first 2 or so matches don’t give me any brown or mostly charge Dragon Soul. If there’s no brown and very little red/purple you’re much better off bailing out and starting over than trying to slowly build up your spells.