This is the normal build I use when I play Illidan. I get Immolation for the extra damage, and Unbound helps with mobility and chase ability. Hunter's Onslaught is good when team-fighting because you have a 50% life-steal without having to use Sweeping Strike, granted you can't heal as much when not fighting another hero. Metamorphosis is good for the bonus stats and for team-fighting with the health bonus you get. Nimble Defender helps with sustaining in a team fight especially because your cooldowns are lowered when you auto attack. Fiery Brand is good for locking down tanks in a team fight because of the percent health damage from it. Demon form is good for the stuns, slows, and roots resistance, the bonus attack speed synergizes well with your Hunter's Onslaught and Fiery Brand.

This is the preferred build if you have a roaming assassin such as Valeera or Zeratul, and is good for priority targets. Immolate can help you reveal both Zeratul and Valeera with the AoE magic damage. Rapid Chase can help you catch up with dashes and blinks/teleports. Reflexive Block helps when your target decides to fight back. The Hunt helps you pick out and get to your targets, and helps to get of the back line of team-fights. Nimble Defender also helps for targets that foolishly attempt to resist. Fiery Brand is good because your targeting one Hero and it becomes easier to get the proc. Nowhere to hide is one of the biggest reasons to get The Hunt. It has unlimited range, so you can dash to team-fights from anywhere. The fact that it shows enemies that are low on health helps you choose who to pick off.