Current favorite revamped after DM change, which made my DK rather useless on Explore:
Queen of Thorns (Woodland Banner)
The 2 Aurai will boost Rowanne’s total damage by 30, which makes for a huge difference in your ability to kill all enemies with one cast. You can predict Rowanne’s total damage by adding twice her armor to the spell base damage. Divide that total by 4 if you want to know what’s the average of the total HP (life+armor) enemies can have in order for them to be killed by a single spell cast.
Start by casting Elspeth on first Aurai (there’s a good chance that, if the summoned troop is green, its spell will be better than Aurai’s, but no need to focus on that, it’s just a detail). That should generate green mana for Rowanne, whose spell you can cast right away, unless you’re sure her spell won’t kill anyone. In that case, you can cast a damage spell with another character (the one you summoned, like – hopefully – a Settite Warrior, of the 2nd Aurai’s spell, which should be cast on the strongest enemy) before casting Rowanne’s spell.
If that doesn’t kill everyone (or if filling another troop other than Rowanne would prove much troublesome), try to match green > blue > yellow (or skulls, if there’s only one weak enemy left) in order to refill Rowanne, or refill Elspeth to sacrifice the other Aurai.
If Rowanne somehow gets hit hard by a spell, don’t hesitate to retreat right away.