too easy on impossible!

[Lancian]

Hey guys,

so, I've managed to get to Zalnaron with my Soothsayer on impossible. This is where all the fun ends.
Yes, I was able to win many deadly to invincible fights mid-game easilly due to Evil Book bug (which is fixed now) and after that by phoenix and hoards of summons.
But now I'm stuck (as his army just one-two hits all my summons) and need an advice. This guy totally destroys my whole army no matter what tactic I use. I've tried almost everything which lead me to find this topic and after some reading I realized, that only Rune Mages I could buy were at the Greenwort castle square.

So, is there anyone who can help me out ? What tactics to use, what army to get (can't get those Rune Mages now), what spells/rage skills I should use etc., to win this fight ?

Here is some info on my current army and stats:

Soothsayer lv 43
19k leadership
20 att
16 def
50 int (+10 with scroll)
60 max rage
105 max mana

125 rangers
60 royal griffs
102 evil beholders
90 demonologists
80 paladins