I found another spell combination that will work - Kamikaze level 2. Coupled with Poison Skull level 2, this spell combination could actually possibly be the second easiest that will work (behind Phoenix).
When I did my original pass through the spells, I had neglected to notice that Kamikaze now works on enemy troops. So I did the "magicbook" cheat and it can work wonders on the Sprites and Werewolves. You may lose a Vampire as you run around the battlefield awaiting the 3-turn delay, but once it goes off - BOOM! It took out half of the 77 Sprites and halved a Werewolf stack - ouch! Then the next round the next bomb finished off the Sprites, Werewolves, and Satyrs. The third round (with the other damage) took the last Werewolf stack down to 4. That was very good use of 30 Mana.
On the Humans, it took out 11 Priests and half the Bowmen! And then the other bomb finished off the Bowmen. Two Level 2 Poison Skulls took out the Inquisitors and then I just had the Swordsmen and Guardsmen left.
This is fairly easy to do.
I didn't even get Diversion Level 1, but it may be possible when you reach level 5 to be able to get Diversion to Level 1, which will make it even easier or go with skills to give you more Mana.
I just got a savegame with Kamikaze, so if anyone wants me to post it let me know (I haven't even started playing it, yet).
So if you get a savegame with this spell, then give it a try!
/C\/C\