Argh that stupid mission, one of the hardest if you are not careful. First off, you need to use the skulls of blight after the naga outpost is destroyed. Then build up to fiends. At the start, Arthas is level 2 so attack the Revenants. Use Anub's locust swarm if you got problems killing them. After both of htem, arthas should be about 3-4. Let illidan take over the 2 obelisks, Arthas should work on controlling the other 2. When Illidan goes for the 3rd one, either let him take it, or fight back. In the first battle, he will summon an Ice Revenant and a Book of the Dead to attack you. Once he falls, then take the obelisk if you only have 1.
It would be optional but wise to destroy Kael or Vashj's bases to avoid attacks on your own bases. Especially when Vashj is base wrecker incarnate and Kael can fry your men with phoenix and himself.
Attack them with the following mix of units, also use this mix to attack the obelisks. Arthas/Anub/Necs/Aboms/Fiends/2 Stats/Dest and optional, meat wagons. This combo of units is better than just massing wyrms. If you want to squeeze a wyrm in there go ahead.
Also the map is littered with expos! There is one north of your start, there is one at each obelisk. One at Vashj/Kael and another on the other side of the map guarded by Illidan's Naga. Have at least 2 gold mines and arm them with towers.
If you do engage illidan, turn on Locust Swarm so Anub won't really need healing. Mana Burn's damage can be blocked by Banshee AMS (for 300 damage) and Dests can "eat" the parasite minions and frost armor he casts.
If you do attack the bases (V/K), be sure you do it when thier heroes are dead from an attack. This cuts off an annoying level 10 from turing the tides in battle, so you only deal with weak naga or blood elves. When thier altars are smashed, they drop somewhat useful items (Amulet of Spell Shield from Vashj, Avenger Helm from Kael). Amulet will protect you from one cast of MB.
After the 4th Obelisk, you win!!!
