Warhammer: Mark of Chaos - Empire Campaign - Chapter 2, Mission 3

Here are general tips for playing the Empire Champaign in Warhammer: Mark of Chaos, on HARD Difficulty. A list of all our Warhammer: Mark of Chaos articles can be found here.
We won't be hand-holding you through absolutely everything, but instead just give tips on situations that we found tricky or that you might not have considered.

Chapter 2: The Hosts of Ulthuan

Mission 3: Into the Under-Empire

Overview

• Long but easy mission.
• Buy every ranged unit you can and fully upgrade their fighting ability, but not their armour if you don't have enough money.
• Use Fire Arrows on the archers to quickly repel the skaven. Don't worry about trying to fully kill each wave, just about surviving with no losses and exploring the map safely.
• Definitely get the Elven Commander because Aurelion can't take point for long with her somewhat low armour rating.
• Buy passive armour-related skills and maximize his armour with whatever gear you have. Put him up front unattached to any regiment, and generally have him stand still and intercept enemies that get close so they do not engage your regiments directly. He should be able to last a long time but definitely support him with all the missile troops you have.
• The Commander does not use his bow unless attached to an archer regiment. Aurelion never has a ranged attack no matter what regiment she is attached to. He and Aurelion can hit at range with their spells, so just use that and let your regiments auto-fire at the enemy.
• If you can delay getting the Commander, you can try maximizing Aurelion's level and then buying him later. New heroes join at whatever level your main hero is when you get them, so the later you get them, the less you need to level them up.
• You can't field a full force of shooters, so take whatever else you can for emergency intercepts and hero backup, although you probably won't need it.
• Creep slowly. Mostly just hold ground and take point with heroes.
• Explore the map first to flush out any Gutter Runners before destroying the crystals.
• Destroying the crystals just stop the lone Rat Ogres that come from around the middle of the map, where the green crystal disks are.
• After you clear the map of other skaven enemies, if you have the patience for it, park your army there and collect XP for killing Rat Ogres until your heroes reach the Chapter 2 level limit of 25.