I found a better strategy for this fight: Use Corefire Imp's Wild Magic like the guide says, but instead of using Terky and the Sporeling Sprout interchangeably, use the Rotten Little Helper. His Blizzard > Ice Tomb > Ice Lance makes quick work of Minixis.
Humanoid Team: Sporeling Sprout (S/B) - x, x, 1. Any breed will work.
Terky (H/B) - x, 1, 2
Any Humanoid with a high damage 1 turn ability
Sporeling Sprout: 1 - Spore Shrooms, Sporeling Sprout dies from Cannon
Terky: 1 - Acid Touch
2+ - Stampede. Terky and Minixis should die together in the same round. If it's not true (I don't see this but just in case) use low damage ability from Any Humanoid to kill Minixis for the first time.
Any Humanoid: 1 - High damage 1 turn ability
As a high damage 1 turn ability I have used Greench's Gift from Rotten Little Helper.
I didn't have Sporeling Sprout, nor Terky, so had to find a new strategy. Used Harpy Youngling (1,2,2), Grumpling (2,2,2), and Kun-Lai Runt (1,2,2).
Use Harpy Youngling with Lift-Off at start, then switch to Grumpling. About the time Grumpling dies, Antaen Cannon will come off cooldown, so switch back to Harpy Youngling and use Lift-Off. Switch to Kun-Lai Runt, and when he dies, use Lift-Off, and Counterstrike and Minixis should be dead.