Pan
Undeads have one of the best initiate spells of the game, called CURSE.
UNDERUSED - TOTALLY.
4 banshees can curse a whole army, and that means that all you army will have an "evasion" rate bigger than a LVL 10 demon hunter. GOOD ENOUGH?
NO? so, there it goes: AMS. there goes your DK, walking freely between their MK + PALLY combo, or mass frosts / chims / gryphons. AMS make mass tier 3 air useless against any army. GOOD ENOUGH? OMG!?
So, you have possession. I'm no telling you to mass banshees.. this is just like a last resort. But possessing like i say, 2 enemy casters, or 2 taurens, or even only their mellee, turn tides, man. it turn tides.
heh, just don't use curse / ams against spell breakers, it's teh *** :ufo