[Executor]

Horrors aren't the best answer to undead, since they have life drain attack which they can't use and fear which won't work since they are mindless, and they are hard to control in large battles.
Now, if all the troops are mindless use soul slay, mind burn, it'll target the commanders.
Communion for Solar briliance.
Living water if it's a cold dominion, it'll make trampler ice elementals
Idealy making a few thugs that cast blood vengeance, or having aegis is the best answer.
But I guess it all depends on what undead you're fighting.