Tactic : how to fight undead ?

[Master Shake]

People have already mentioned buying Priests. Treat Priests as elite units. They cost less than most single cavalry units. Have a minumum of 10 per army. They are also great for driving down Ermor dominion, which determines how many units Ermor gets.

Your main goal should be to keep your priests alive and banishing for as long as possible. Get some meat shields in front of them. Summoned mindless units are perfect (vinemen, vine orges, Mechanical Men, your own undead, etc.). Heavy in fantry works well too. Your biggest worry for your meat shields is that they will rout.

Get a bunch of archers too. I prefer archers over crossbowmen versus Ermor, since penetrating hogh protection armor is not the main problem. Massed archers even work versus Soul Gate, since ethereal units have very low protection, and 25% of missles get through the ethereal.