Agony + spamming the "fire something" lvl 1 astral spell with the 2 astral mages. Those 2 got killed by your arrows (and of course, died). No problem on that part.
I don't really know how it scales, though, but area and damage have a little + beneath them. So area should have gone from 3 to 7 or 8 given that the caster should have been lvl 8 instead of 3, killing a few dozen units twice (I scripted it twice) and causing a huge morale breakdown of anything it hit, resulting in routing of most of your forces. The fire mages + wyrm should have finished the remnants.
Sadly, as you have seen, I tried to rely on indy archers (forgetting that their morale was 7 and they fled after taking a shot, causing my entire force to rout) and the communion failed. I thought they would hold for a bit more... Both of those of course caused a defeat. Furthermore, a minor horror showed up (murphy's law) on turn 3 and proceded to try to kill my hero (but failed).
What did work, however, was my wyrm holding your melee forces while my fire mages helped her kill them.
I made several mistakes I won't do next time. I should just have gone for the 1S 2B instead of the 1B mages and commune. I shouldn't have relied on those archers but they are the only ones I've got access to. As far as mages go, I wanted to buy the 1S 2B massively after I got boots of youth, but I shouldn't have held back.
That's the battle report !