yeap Zhuangzi is very right with this sneaking here and there, sniffing loots, gathering more powerful troops and then strikeback
you can also consider army especially for undead troops, like I did (and had a way easier way through Land of the Dead).
I gathered (as 19lvl Warrior on Normal):
-stack of Inquisitors
-stack of Priests
-stack of Unicorns
-stack of Black Unicorns
-stack of Royal Snakes (my must be since I got feanora froggy, two royal snakes rings and snakes boots)
first four has bonuses againts undeads. you can also get some items like silver rapier (I think everyone can get this in trade for some runes but IMO it's not worth it) or sword of light (nice thing which I used
). You can also equip both of them in the same time. I don't know other helpful in this task items.
basically I opened battle with Phantom on Inqs, phantom using holy anger at priests (with this buff their massive), than shoot at ranged units, wait with my melee units for an enemy and attack. sometimes I use timeback on phantom and in second turn cast holy anger at snakes but I rather cast one more time phantom and holy anger with it, other phantom can attack. because of lack of shamans and their totems i used a lot of phantoms, deamon gates, ice ball to minimise loses. also unicorns as tanks (target them) works fine if money is not problem for you and you have lot of them in reserves.
btw anyone knows if Land of the Dead counts as a night? for nightime operations and miner's helmet bonuses?