Warhammer: Mark of Chaos - Chaos Campaign - Chapter 2, Mission 7

Here are general tips for playing the Chaos Champaign in Warhammer: Mark of Chaos on HARD Difficulty. At the end of Chapter 1, Mission 6, we chose Nurgle instead of Khorne. 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 Wrath of the Rat-Kin

Mission 7: To Catch An Elf

Overview

• Before you start this mission, be aware that at the start of Chapter 3, you will not have access to a full camp and cannot buy or upgrade regiments or heroes for a while. The Skaven have an easy mission before reaching the first camp, and their regiment selection changes. Overall, be sure you have bought whatever heroes, regiments, and gear you want before entering this mission.
• After winning this mission you will immediately be moved to Chapter 3. This is the last chance to buy artifacts from the stores.
• You can buy two heroes in Chapter 2, but only bring a third hero in this mission. You cannot buy any heroes in Chapter 3, so get them now. In Chapter 3, you can field a third hero but you might as well get all the heroes you can now if you have the gold for it.
• More heroes also means a bigger mana pool, even if some heroes don't use the mana at all.
• If you don't use a hero right away, don't allocate their skills yet, in case a specific mission later makes you change your mind.
• There is an optional objective to destroy 10 city buildings. You receive this objective as soon as you enter the city. If you destroy all the buildings you get some gold and a couple of potions. It is not clear what fulfilling the objective really gets you as there is no special acknowledgement or reward for it.
• The level limit for your Chaos heroes is 25. If possible, reach this limit for at least your main heroes before moving on.
• Your best bet for getting to the level limit was actually in Chapter 2 Mission 2, the end of which was also the last chance to get the first hero available for purchase in this mission. Heroes start at the same level as your protagonist (Thorgar, or Kasqit, depending on who buys the hero), so the higher your level when you buy them the better, as you would then not have to level them up as much.
• There is a hidden "time limit" in this mission: Once you have gone far enough into the city or destroyed enough buildings, it appears that the elf mage is scripted to move toward you. If you haven't destroyed all enemy regiments, you won't get a chance to do so because the win condition is defeating the elf mage, and once he comes for you, you can't really keep running away forever.

Walkthrough

Phase 1 - Draw fire and survive the initial attack wave

• Although Thorgar makes a big deal of the one enemy cannon, taking it out is not your immediate objective. If you rush it, you could be surrounded and suffer heavy losses.
• Your sorcerer and whatever unit you have attached the sorcerer to can survive bombardment fairly easily because there are so many enemies to Steal Soul from. So, as always, we use it to draw fire.
• Keep the other regiments far back. The enemy cannon might still take shots at them if the sorcerer's regiment is engaged and the others are not (presumably to avoid friendly fire).
• We need to draw attention from the cannon so that our Hellcannon can take it out.
• Watch for a regiment of knights coming from the west to flank you. They leave from the western exit of the city, which is initialy in the fog of war.
• Turn Stand Ground ON for your own cannon. Otherwise it will target the nearest enemy regiment and start firing (which could be an enemy regiment you have engaged in melee, thus blowing up your own troops). Focus fire on the enemy cannon.
• Also, do not target the handgunners near the cannon as we'll need them later. Some might be blown up because artillery is inherently inaccurate, but there's nothing we can do about that unless you want to take out the artillery with troops. Set your cannon to stop (click the shield, and make sure Stand Ground is also off) once the enemy cannon is destroyed.
• As an alternative, you can go to the far west and head up the western entrance, but the cannon can turn around to shoot at you inside the city anyway.

Phase 2 - Regroup and refill regiments

• Once the Empire cannon has been destroyed, bring up your reserves, kill all enemies outside the city, and then STOP. Pull back.
• No more enemies will come out of the city. There is a patrol and some guards at the entrances, but nothing scripted to come out yet.
• Your new immediate objective during this period of calm is to attach your sorcerer to any regiments that have lost models, and use Steal Soul to resurrect the dead.
• The handgunners at the entrance will not move from their location unless bombarded by a cannon, and Steal Soul has a longer range than their guns, so use them to recover your losses while they stand around and have the life sucked out of them.
• If you use this on melee regiments they will come after you. If you need more resurrection with Steal Soul, just run away until your spell cooldown has ended.

Phase 3 - Optional objective

• Advance to the city, clear out the defenders at the entrances, and start destroying buildings.
• After a few are destroyed, the elves will all come out whether you could initially see each other or not. Having to handle them and killing the elf mage (which wins the scenario) will probably stop you from finishing the optional objective, but that's okay since it doesn't look like you get anything for completing it anyway.

Phase 4 - Defeat mage and win

• The mage is low-level and you should have an overwhelming force compared to the elves. Win, watch the cutscene, and be transported to the start of Chapter 3.