Play against Necropolis.

(I want to note right away: we will be fighting on the largest map possible).

The conclusion is: he has no chance, because he won't be able to rush you. The game will definitely reach at least the mid-game, and most likely the late-game... well, you know what Orcs are capable of in the late-game ;)
Against him, I think you should focus on:
1 - Attack (tactic - Battle Fury - Stunning Blow)
2 - Suppress Spells
3 - Leadership (Rally Troops - Aura of Swiftness - War Cry)
4 - Luck
5 - Battle Shout
6 - At your discretion
Machines are not needed. You can take Suppress Darkness if you are sure you won't miss. Attack and Leadership are a must!!! And definitely in the order specified, so that due to the tactic and Aura of Swiftness, you can already deal one hit at a time and reach the Liches, who will deal less damage up close.
There are no restrictions on the army, just level up and that's it...
Best heroes:
1 - Krag (already has Attack with Battle Fury)
2 - Goshak (due to Mega Evil Assassins and Reinforcements)
3 - Shakh'Karakut (for the late-game with Wyverns and Defense)
Just level up thoughtfully, and the Necromancer won't have a chance ;) That's the whole trick...

Good luck in battle. Scatter him across the graveyards :smile19: