undead vs night elves 6

W I L L - O - W I S P

Just cast Unholy Frenzy on the Elves' lumber-harvesting Wisps. Wisps only have 120 HP, so they'll die from the spell (unless they're next to a Moon Well). Even better, the Night Elves don't dispel effectively. Doing this doesn't trigger an "under attack" warning. Most of the time, players won't notice their Wisps dying off until they're short of lumber.

Just to add to that, if you have a Human ally, have them cast invisibility on the Necro, rush him in, cast it a few times, and rush out. Take that!