depends on what u want
u could go for rune magic level 3 for winter circle
or go for order level 3 which is cheaper
and cast alot fo healing (it damages undead)
you have 3 options to do this battle
(one will be splitting soothsayers and get beserkers/vikings(for beserk ability)/slinger/axethrowers(you can replace slinger for ancient bear but sometimes if u get lucky he will cast doom/sheep on your slingers) which cost alot of mana
and then spam call of nature and GET very lucky he aim with offensive spells on those
option 2
Try to kill at least one medium/big stack really fast and pray that he will USE call of necro instead of an offensive spell
option 3
mass offensive spells(mainly winter circle
try to kill as many with your spells and wait and then rush in with beserkers vikings and hope they slaughter the minor stacks (and keep in note to kill the FAST INI units first (cursed ghost, ancient vampire,vampire(vampires in bat form, necromancers
rest is total bullshit
if he gets alot of skeli archers
like 70+ restart game there is no way u can beat that