Zacen:
You have 5 backstabs and an archer.
You do not have the ability to kill GreatWyrmGold's troll with your remaining units, no matter how hard you try or how cleverly you plan. Your assassins have a total of 5 backstabs in them for a total of 20 damage. The troll as 30 hp and is unlikely to move out of the dense vegetation protecting it from your archer.
You can just barely kill GreatWyrmGold's necromancer-cleric cluster. Each turn, he can summon a skeleton between your archer and his necromancer. You need two backstabs to kill a single cleric and must either kill both clerics (a total of four backstabs) or distract three skeletons out of four somehow in order to force him to leave a tile adjacent to the necromancer open for an assassin to get the backstab in. This will not leave you enough resources to kill anything else, but you could do it if it came down to just your units vs. them.
You can kill his mage. You just need two backstabs, or a single backstab against the skeleton blocking your archer and a shot with a poison arrow on the mage that doesn't get cured. This is super risky, since him moving his mage or his warrior into the correct position will ruin this plan.
You can kill his warrior or any one of my units using two backstabs. At best you can kill 2 such units this way. You can also shoot them, but you don't have the firepower to take out enough of my clerics for this to do permanent damage, and GWG will be constantly shotblocking any attempts vs his unit with a skeleton.
The only winning situation for you is A] for me to kill GWG's necromancer, B] for me to kill GWG's troll, C] for there to be no more than 1 cleric remaining on either side, and D] for me to lose at least 2/3rds of my remaining beserkers and E] for you to make no mistakes at all.
The obvious response to this is for me to pick the Zacen-cannot-win-while-this-lives unit that is least threatening to me (GWG's unkillable-with-assassins-but-easy-to-handle-with-hasted-beserkers troll) and leave that alive until you agree to play ball. So I'm going to do exactly that:
Precommitment: GWG's troll does not die Zacen kills some of GWG's units.