I got +650 leadership at level 14, so I filled up on Inquisitors and Beholders, cleared out the Eastern Islands including Lucky James and Duke Sov. Surprisingly, the quest related battles are easier than the random armies that you need to clear to get to them.
So it was finally time to go back to the Orc Embassy and prove my manhood. I decided against using Cursed Ghosts this time and went with:
Beholders
Griffins
Royal Thorns
Royal Snakes
Inquisitors
I also used a charge from my mask of rage artifact (+20 rage) for the first time, up until now I haven't had to use any potions or anything. The problem with the above setup is that I don't get to go first so I couldn't lay down a trap. The enemy hero also had an annoying habit of using magic poleaxe on a different stack every turn, so I had a ton of resurrecting to do. However, I came up with devious and exploitative strategy.
I got the enemy down to 1 shaman, and let him keep his healing totem. Using my ample stacks of thorns, I put magic spring on one and attacked the shaman, who countered and I got my mana back. I could repeat this endlessly except sometimes the shaman would attack me back or use the axe dance and I would get an additional 5 mana. He would also heal himself to full every turn so I didn't need to worry about him accidentally dying. Endless mana loop to resurrect all my troops.
So I filled my rage and mana before I finished off the shaman, bought my own stack of shamans and went into the basement for some fun. This is the fight with the stack of 1400 fire dragonflies. Again, I lost a couple units from every stack, so to generate mana in this battle I used my beholders to put the dragonfly stack to sleep turn after turn, put a poison cloud on them, and then put my mana springed (sprung?) thorn stacks inside the cloud. You gain 5 mana every time they take poison damage, so your mana spring is guaranteed to pay off in full. This is another exploitative but very necessary strategy for the hardest battles.
So now that I have Royal Thorns and Shamans, it's time to go sink all the pirate ships and make the oceans safe for mass murdering heroes like myself.