Under the Burning Sky
This chapter is a tower defense mission where you must keep Kel’Thuzad alive for 30 minutes while he summons Archimonde. You’ll really get pushed hard towards the end so build as many towers as you can before the end.
Archimonde – Keep Kel’Thuzad alive while Archimonde is summoned.
Goblin Land Mines – Find the Goblin Land Mines.
1) Ring of Protection +5 is dropped from an archmage to the north of Kel’Thuzad.
2) In his tent is the Tome of Strength +2.
Under the Burning Sky Walkthrough
You’ll want 6 to 10 Spirit Towers to the north and east before the final onslaught and close to that number to the west as well. You’re limited by how much gold you have available so you’ll need to preserve resources and not let your towers get destroyed early on in the mission.
During the course of the summoning you’ll be gifted with units. I preferred to keep these units next to Kel’Thuzad and use them as his own personal body guard. You’ll be given first Hellhounds and then Infernals. If anyone breaks through your towers they’ll be there to protect Kel’Thuzad.
Make sure you have a spare acolyte who’s set to auto-repair on each side to repair the towers and keep them from being destroyed.
If you can hold out to the end you’ll complete the Undead campaign and be ready to move on to the first chapter of the Night Elf campaign, Enemies at the Gate.