the eggs in one basket unit if you will. In my case it was a unit of 18 Grave Guard, with great weapons, Full command, The hatred banner, a Vampire with Avatar of Death, walking death (+1 combat res), battle standard and the regen banner and a Wight King with the Sword of Kings (K.B on a 5+) and the accursed armour (+1 T, -3 I and -3 Ws), even with a dead general they rarely take enough casualties to worry after their Ld 9 crumble check with a regen.
up against a unit of 50 Skaven Clanrats, a screaming bell with a seer on top and two warlock engineers and a bunkload of doo dahs. they were unbreakable so not a lot i could do, we decided to just keep playing until the armies had destroyed one another. end of the game had a unit of 20 slaves and my wight king and vampire with one wound and the Grave guard standard still alive