Battle against Karador on impossible

[Metathron]

I am perplexed at how some folks manage to do this battle with no losses. In all my previous games (normal or hard) I usually suffered heavy losses, but this time around, I just had all my troops killed with some rather huge enemy stacks left.

My army consisted of elves, evil beholders, sprites, dryads and ancient treants. I cast the ice spirit's shards at the beginning to stall enemy walkers, so my shooters could shoot. Well, for the couple of rounds I was able to shoot, they didn't do much damage. I'm thinking shooters are not a good choice for this battle. Better get some sturdy walkers/flyers, maybe griffins. Any recommendations?

My sprites/dryads had fear cast on them for most of the battle. An outstanding moment was when my sprites helped the enemy destroy the barriers between us.

I also cast fire rain several times, but against such large numbers, it's more like fire drizzle.

I also remember someone mentioning a strategy with emerald dragons and invisibility, but I can't seem to find it, and I don't know how it goes. I'd be willing to try it, just to avoid getting slaughtered by this ridiculously enormous army.