Alright... hmmm...
Witch Elves are a very effective killing unit with a fatal flaw: frenzy.
Our Core is never meant to win combats, but to stall them. If the enemy is so overwhelming, then using large-sized units (like Zombies) is not an optimal choice, since they'll get hacked apart as easilly as 5 Dire Wolves. That's why redirecting is the prime strategy to use against Witch Elves.
Now, that is only a part of the whole problem, since our purpose is to defeat it, either by destroying the unit or winning the game by leaving it untouched/controlled, then I'd recomend the following:
- If that Unit is on the flank, then you have a bit of an advantage, since it will not be able to engage the middle line if you redirect it properly. Even without a tooled up list to face them, we have Dire Wolves and Skeleton Riders as cheap maneouverable units that can just stand in front of them, angled "away" from the main battle so that they must either reform (and pass their frenzy ld test, which is easi for ld 10 elves) or charge the meager 5 wolves and overrun further away from the battle. That's your tactic no. 1.
- Now, while redirecting, your opponent may anticipate the cheap
chaff you'll throw at them and attempt to reform said unit, while targeting your
chaff with either shooting attacks or spells. This is perfectly fine, as long as you can weather the damage inflicted. You should be positioning your own strike force (of, perhaps, Black Knights) right where they need to be, closing in on expensive stuff, or the Witch Elves themselves. To counter the unit reforming and then re-engaging the middle fight, consider using Fell Bats as well as Dire Wolves. They can dance all around a
Horde, while forcing them to a uncomfortable charge with ease.
- Dealing with the
Horde itself, you can use any number of "safe" ranged options to grind them down to a more manageable size. As far as undead Legions is concerned, The Net of Amyntok and Usirian's Vengeful hex (don't know the name in english, I have the spanish verson of the
TK book, hehe), are quite good at holding the unit back or decimating it. Curse of Years is another tool, despite their Ward Save and Magic Resistance, it will cause some wounds, plus it will draw some dispel dice. Usirian's Hex is particularly good, because of the negative movement stat and the dangerous terrain test.
- Finally, if we are to compare might against might, consider using a 50+ Skeleton Archer unit with Khalida in it, and just shoot at those T3 Elves, coupled with anything that can debuff T from Lore of Shadows or Death. They should get weathered down rather quickly and become much more manageable once they've received 3-4 volleys. Pair this up with
chaff to get much more damage inflicted on them while redirecting them.
All of the above requires you to sacrifice units (even important units, like Varghulfs or Terrorgheists) for the sake of redirecting it into a trap and grinding them with vampires or such. Don't play as you would another army, and plan your moves carefully, and most lists should have a way to deal with deathstars such as that of Witch Elves. I speak of experience, no matter how powerful a
Horde is, if it gets flanked and has no way to deal frontal attacks, it is doomed to break or crumble away, even against sub-par warriors, like ours. Static Combat Resolution plays a big role, and having an advantage of +4 (3 ranks plus, at least, flank combat) is nothing to laugh at, specially with so few returning attacks being made, regardless of how many a Witch Elf can dish, they eventually lose.
I hope this helps, and gives you many more ideas of how to defeat an "invincible" enemy
