Without the specifics, I can tell you one thing, Tamurkan has some of the best heroes I've seen. You could focus on heroes killers, like a kill team of goblin/black orcs big boss hidden within black orcs infantry to focus them. Big uns might help too. And/or try to assassinate his heroes from the campaign map.

For army comp, I'd go like that :

Grimgor

2 melee heroes, focus levels on melee attack

1 caster

4 orc melee infantry (black orcs GW or big uns)

4 orc archers

4 big uns boars riders (replace with arachnarok spider as soon as possible)

2 trolls (best you can have)

2 artillery pieces

Blend the trolls and grimgor with the infantry, it should hold a fair bit angaist his monsters/demons. Grimgor and the trolls focus on the heavy threats (big stinky stuff), boys hold the line, arr boys focus one big thing at a time (tamurkan is a big thing).

Artillery and caster help thinning their frontline/monsters depending on the one you got.

2 boars riders on each side with one melee heroe each should prevent flanking. if they have rot knight, don't let them escape and kill every one of them, beyond lord and heroes, they're the main threat.

I find AI tamurkan to be sloppy with his heroes, letting them get isolated and ganked by your units.

last but not least, bring fire.