Warcraft 3 Frozen Throne Walkthrough for Undead Scourge:
Chapter 2: The Flight From Lordaeron
Main Quest: The King's Exit
First, kill all the ghouls that are attacking Arthas, obviously. Next go through the gate. You'll receive a pair of necromancers who will be invaluable in this mission. A ghoul will also be with them. Hotkey all your permenant forces into one group while the summoned creatures head north. Of course, grab the goodies in the ground. There isn't anything very useful here, however, as potions are almost pointless. Arthas can gain health easily using death pact on a summoned skeleton. In the north room, there is a throne where the enemies are guarding a scroll of protection. Break open the pedestals with books on them to gain a tome of agility and intelligence for Arthas. Head to the east, with your summoned skeletons in front. Take out the two abominations then head south. There will be some minor fighting here, and it's especially easy with your summoned creatures in the front taking the brunt of the attack. Work your way all the way south and kill the creeps to get a ring of protection +2. Head back to the main path and go east. There will be a minor skirmish, and you'll receive the aid of an abomination.
Head further north to find a dreadlord guarding a pair of crypt fiends in a cell. Break them free to enlist their aid. Head north all the way from here to fight a big battle with lots of summoned skeletons. Kill them all then grab the Claws of Attack +3 for Arthas. Go back out and to the west. When you get the shade, head a little south and look for the lowered section of floor to the right side of the screen. There is a switch for this, which we'll get to now. Go to the northwest and crash the gate, then stand on the glowing switch. Head back and the floor should now be passable. Inside are boots of Quel'thas +6 (agility bonus, very nice). Return to where you were and go west until you reach the barricade. Smash the barrels first to allow your forces to go through and fight the crypt fiends. The ghouls behind them will join you when Arthas approaches.
Optional Quest: Meat Wagon Surprise
Go directly north until you can't any more, where you'll fight another dread lord. Kill him then go to the west to gain an abomination. Smash the gate to the south to get a pair of meat wagons. Put them in their own group if you like, just don't leave them behind, ever! The undead send out too many ambushes. There are 50 gold coins to the north if you care. I didn't bother. Head east and go through the gate. Be careful here, as the two towers along with the undead guarding them could cause you your first loss if you aren't quick with death coil. When everyone here is dead, step on the floor plate.
You will find an Orb of Venom for Arthas. Pick a terrible item and take this instead. I chose to ditch the voodoo doll. The gate here is invulnerable, so head to the east. Kill everything along this path. You'll eventually reach a point where the previously locked door opens and you get ambushed by some extra undead. There is a rune of the revenant to be found here. Use your revenant to go ahead of your army. Head south through the door and to the west. Follow the path and keep the Frost Revenant in front to take the damage. When you reach the door guarded by two spirit towers, first go east and break the ghouls out of the cage, then go west and grab a tome of strength and second rune of the revenant. Put this new revenant in front then go through the gate the towers were guarding.
There are a lot of Undead here, but thankfully some of them are yours. Grab the abomination for sure and put him in your group. You may be full and need to make a second group if you've done well in this chapter. Break down either of the gates and go through. Kill off the necromancers then summon some skeletons from the corpse pile and send them all east. Follow with your army and kill off the doom guard here, then go north and destroy the crypt. Hit the gate to the west to be in the last section. You will fight a huge abomination named bloodfeast who is way weaker than he looks. Kill him off and go through the north to finish the mission.