Let me start off by saying that Illidan is by no means an easy hero to pick up. In order to even stand on equal ground against most heroes, you have to outplay the opponent significantly. The best way to succeed as Illidan, is to play towards your strengths.
In a 1v1 scenario, Illidan excels in extended trades. His passive grants him significant uptime on Evasion, allowing him to sustain himself with his passive lifesteal.
When teamfighting with Illidan, use your incredible mobility to weave in and out of combat. Don't overextend into the backline, or you'll find yourself dying before you're capable of dishing out any real damage.
While Illidan is capable of laning in a 1v1, he's much better suited to a 2v2 lane, so he can step out and solo mercenary camps while still having a teammate to soak experience from the lane.
Illidan is capable of soloing Knights as early as level 4, making him incredible for sneaking early objectives. I repeat, Illidan is by no means an easy hero to pick up. However, with time and practice, you can become a force to be reckoned with in no time.

Battered Assault

While a decent talent choice, I personally never take Battered Assault. While the buff is active, Battered Assault provides approximately 12% increased DPS and 2.4% increased lifesteal. This talent helps increase Illidan's mediocre early game damage.

Shadow Shield

My personal favorite of the T1 talents, Shadow Shield is required if you plan on clearing early mercenary camps. This talent also allows you to trade efficiently early against spell dependent champions and allows you to sustain yourself longer in late-game teamfights. I would take this talent in almost every situation.

Regeneration Master

Don't ever take this talent. It's trash.

Seasoned Marksman

If you plan on taking an offensive T1 talent, my recommendation is Seasoned Marksman. While taking this talent makes Illidan's already weak early game significantly weaker, the damage scales up rather quickly. Taking this talent inhibits your ability to do solo mercenary camps, but increases your late-game dueling potential significantly. I would take this talent if the enemy team has low burst damage, but high-health tanks that need to be mowed down.



Marked for Death

Marked for Death is the best talent choice in T2. The burst provided from the critical auto significantly outweighs every other damage option and is by far Illidan's highest damage increasing talent while also increasing his lifesteal potential.

Fel Reach

An additional 20% distance on Sweeping Strike is incredibly unnecessary due to Illidan's already incredible chase/disengage potential.

Immolation
I see too many Illidan's taking this talent. While it increases Illidan's AoE potential, it decreases your ability to pick off and assassinate targets which is Illidan's sole purpose. Later on if you choose Second Sweep from T6, the DoT from Immolation actually munches itself, lowering your damage potential even further. While this talent is not unviable by any means, it is a significant damage decrease. This talent however, is fantastic for early mercenary camps.

Thirsting Blade

I find that T2 is too valuable as an offensive talent tier to warrant picking up Thirsting Blade.



First Aid

This talent is 100% mandatory to survive as Illidan. No other talent in this tier is worth picking up. First Aid is not only incredibly valuable in winning duels, but also gives you to opportunity to bait your opponents into an unfavorable engage.

Thrill of Battle
While I would never take this talent, I felt it necessary to include in my guide to explain my reasoning. While it does seem like it could be an attractive talent, Illidan's base attack speed of 0.6 already allows him to take his spells off of cooldown incredibly fast. At most, this spell will allow you to utilize your Heroic Ability more often, however, you will seldom find a scenario where your Heroic Ability won't already be off of cooldown when you need it.



The Hunt

This spell is Illidan's bread and butter. It is, realistically, the only reason to pick Illidan as he currently is. Illidan functions best in a catch comp, and The Hunt is far and away the best catch spell in the entire game.
This Heroic Ability allows Illidan to capitalize on an enemy who is out of position, allowing his team to follow up shortly afterwards. This spell also allows Illidan to escape from certain death situations by jumping to a minion in another lane, freeing himself from any enemies attempting to pinch him.
Come late-game, this spell lets Illidan pressure a separate objective from his team, forcing the enemy team to split their focus. If utilized correctly late-game, The Hunt cements victory in otherwise close games.

Metamorphosis

Many people would consider Metamorphosis to be Illidan's teamfighting ultimate. While this is true to an extent, I find The Hunt to be a better ultimate for teamfights due to it's incredible engage and burst potential. As such, I would not take Metamorphosis over The Hunt as a teamfighting ability.
Metamorphosis' redeeming factor is that it allows Illidan to solo Grave Golem, which is a feat he cannot typically achieve without it.


Giant Killer

This talent is fantastic, especially when coupled with Illidan's 0.6 base attack speed. If you find yourself wanting to do more damage, take this talent.

Friend or Foe

While this is a pretty cool talent, Illidan already boasts the mobility to escape almost any scenario.

Unbound

Like Friend or Foe, this talent is simply unnecessary.

Sixth Sense

My personal preferred T5 talent, Sixth Sense allows Illidan to soak an incredible amount of punishment. When paired with Shadow Shield, this talent essentially makes Evasion the single best damage mitigation tool in the game. With this talent, Illidan is capable of dueling any equally leveled hero in the game.
If facing a Nova, this talent is mandatory.



Second Sweep

The best talent choice in this Tier. Second Sweep provides Illidan 100% uptime on his Sweeping Strike buff, increasing his sustained damage and mobility to absurd levels.

Blood for Blood
An incredibly overrated talent. Illidan does not boast the burst to sufficiently use Blood for Blood's %max HP nuke, and already boasts the chase/disengage potential to never require the slow.

Hunter's Onslaught
I wouldn't recommend this talent in any scenario. Illidan's spell damage is incredibly low, as the vast majority of your damage comes from your auto-attacks.

Stoneskin

A pretty useful talent for soaking punishment. If for some dumb reason you decided to take Metamorphosis, take this talent as well. If you took The Hunt (which you should have), you should ignore this talent in favor of Second Sweep.



Nowhere to Hide

This is your go to Level 20 talent. This talent gives Illidan incredible map presence, allows him to escape from any gank, and when coupled with his passive, lets him traverse the map as he pleases while also having his Heroic Ability off of cooldown shortly afterwards.
This talent is not mandatory, but it is by far your best choice in most situations.

Bolt of the Storm

This is the only other T7 talent worth taking. Take this ability against wombo-combo dependent comps such as Gazlowe/Falstad. This instant blink allows you to correct any error in your positioning, and can even bait out and waste enemy Heroic Abilities. If come late-game you still find yourself dying too often in teamfights, take this talent.

While Illidan has a rather weak early game, his kit can be easily manipulated to win trades. Only trade if Evasion is up, and back out before it falls off. When done correctly, Illidan can avoid all damage from trades, while dealing approximately 210 damage at level 1. While you'll likely never kill someone in lane, you can harass them off of objectives and force them to give up experience. While they're back in base, Illidan is incredible at sneaking mercenary camps or roaming to other lanes for a quick kill.






During the mid-game, Illidan functions best when grouped with his team. Keep your eyes on the map looking for targets that won't be able to escape you, such as Nova, Gazlowe, Nazeebo, and Sgt. Hammer. Don't open a teamfight with The Hunt unless your team is close enough to dive in to the back-line with you. Try to position yourself in a way that a single Dive will put you a safe distance away from enemy threats. Use your double Sweeping Strike to weave in and out of the fight, and make sure to hit at least one target, granting you the increased basic attack damage.
At this point in the game, you and your team should be aggressively targetting enemy objectives, attempting to catch them while they're doing Grave Golem or a map objective. This gives you the edge in the teamfight, allowing you to easily pull off a clean ace.






Come lategame, Illidan needs to focus on ending the game as soon as possible. Hop in a lane opposite of the objective your team is contesting and start to push. Take any and all nearby mercenary camps, and kill any fool who dares challenge your might. If you find yourself being pinched by multiple opponents, use The Hunt to join your team at whatever objective they're pushing to easily secure it with a man-advantage. If your team isn't currently on an objective, you can use The Hunt to hop to a minion in an opposite late, bringing you to safety. Keep your eyes on the map for the shimmer of a stealthed enemy, and try to engage on them before they're capable of engaging on you. Stay aware of the enemy's chosen T7 talent in a 1v1 scenario, and make sure to save your Heroic Ability to re-engage if they attempt to escape with Bolt of the Storm
Don't be reckless with The Hunt, but also don't be afraid to use it. If you continue auto-attacking targets, it will be up in no time.

Haunted Mines is without a doubt Illidan's worst map. It's the smallest map, so he doesn't gain too much benefit from his global presence, he can't jump into the mines with The Hunt unless he's already jumped in the mine shaft, he doesn't have a chance to solo any mercenary camps early, and he needs to spend several abilities to clear skeleton packs. The best way for Illidan to win on this map, is for him to play with his team. You should enter the mines with all 5 teammates as soon as they open. Clear as many small packs as you can before the inevitable team-fight. Keep your evasion off of cooldown in the mines, there's no telling when you're going to need it.

After the first mines push, win or lose, rush Knights with all members of your team. Your goal here is to either capture the camp before the enemy team has time to react, or kill the enemy team while they attempt it. Afterwards, if your golem is stronger, you're going to want to push with it.

When the second mines is starting to open, there shouldn't be any objectives left on the map to take. At this point, you want to group with your team in the mines before the skeletons even spawn. This allows you to take a headstart in taking skulls, which can make or break your next golem push. Rinse and repeat your mercenary strategy, and prepare for the final mines.

The third golem is absolutely essential. 99% of games can be ended on the 3rd golem, even if you have 0 skulls. In most situations, defending against the 3rd golem is a bad idea. If you have a stronger golem, push with it and focus the core. Even if you have a weaker golem, if you have the ability to base-race, it's a good idea to do so, as you'll probably just lose if you attempt to defend against the 3rd golem.




Early game in the Cursed Hollow, you should two man your team's mercenary camps before the first tribute spawns. This gives you lane pressure, easily coaxing the enemy to give up the Tribute. This can net you an experience advantage, especially in solo queue where the enemy team may not be coordinated enough to back off of the tribute completely, netting you several kills worth of experience, or even an early for if they choose not to deal with the pushing mercenaries.

I find Tributes to be a much more strategic choice than any other map objective. Don't be afraid to give up a Tribute to take several mercenary camps, or to make a strong push on an isolated fort. Giving an enemy 1/3 Tributes isn't a big deal, and even 2/3 can be given up in certain situations.

If you find yourself in the position to win a teamfight, and the enemy is pushing for their third Tribute, giving it up entirely can actually be beneficial. During the enemy's curse, use your superior teamfight to secure a man-advantage and take the enemy's mercenary camps before retreating to deal with the advancing waves. If done correctly, you can bleed out the enemy's curse completely, wasting all 3 of their Tributes, and forcing them to restart their progress.




Dragon Shire is one of the most rewarding maps for strong teamplay, however, it's size makes it one of Illidan's weaker maps. This is not to say he's useless on this map however. As soon as you hit level 4, you should gun for a Knight camp. This grants you the pressure to take your shrine quickly. If possible, try to lane with either a strong duelist healer such as Li Li or Uther. With a strong healer, Illidan can actually win 2v2 fights with ease. Don't be afraid to commit and seriously stick in a fight. Your vast mobility can allow you to leave at the last second, and the longer you stay in the fight, the higher your chance to win it.
If your team can take the first Dragon Knight, group mid and push. Start backing out BEFORE the Dragon Knight dies, or the member occupying it will likely get pinched and die against skilled opponents. As soon as it dies, your team as 5 should swing up and take the enemy's Knights.

In the downtime between Shrine spawns, you should contest the enemy's Siege Giant spawn. If you can take the enemy's Siege Giants on this map, you're granted tremendous pressure bot. If you're capable of taking all Siege Giant camps at once, your 6 Giant push can force the enemy to give up a Dragon Knight entirely.
Keep in mind that the longer the game goes on, the stronger the Dragon Knight. Even if behind by several forts, a 25 minute Dragon Knight can easily push to win. Don't give up hope on this map, one late game teamfight can easily secure victory for you.





******* I hate this map. Despite the boiling rage I feel towards this map, it's definitely one of, if not Illidan's single best map.

This map is absolutely gigantic. Come level 20, this means you essentially win with The Hunt. Split push that bottom lane until the enemy team tries to send a few heroes deal with you, then ult on some poor sucker in the top-lane and have your team follow up. This map is so incredibly easy to pick people off on, even against incredibly coordinated teams. Early game, this map has mercenaries galore, which is essentially Illidan's wet dream.

If you can sneak the enemy team's Knights early game, rotate down to their Siege Golems on the other side of the map to snag those as well. As the enemy team deals with both pushes, you're left open to grab all of your own Mercenary camps, then focus on snagging seeds for your Plant Horror. DON'T reach 100 seeds. If you do this, your Plant Horror will spawn and wither in 60 seconds and all of your effort will be for nothing. Try to sit at around 95-99 seeds and only take your Terror if you accidentally force it to spawn. The reason you typically don't want to take your Terror early game is because it's tremendously weak. It was recently buffed so it's not nearly as useless as it used to be, however early game, I still consider it a waste of time to take. Come late-game, like all late-game map objectives, this thing hits like a truck. Try taking it around 15:00 minutes or so and hard push a side-lane for your team. This can net you multiple forts, especially if you're already ahead.





This is easily my favorite map. Not only is it a strong map for Illidan, but it also has the highest skill-cap for him, making it incredibly rewarding when played right.
When the gates open, you should rush as 5 to the Smiley Face (Also known as KJ, or Kevin) and contest for vision. As Illidan, you want to stay long enough to secure the watchtower, but you need to be heading bot as quickly as you can to soak experience. There's a fine-fine line between leaving too early and too late. Illidan is capable of taking chests incredibly quickly, and can outduel the vast majority of heroes who will try to contest it.
At level 4, if you have the opportunity to sneak bot Knights while someone holds the lane for you, this can grant you an early advantage. If you suspect the enemy is taking their Siege Giants, this is the perfect opportunity. After snagging bot Knights, head to your own Knight camp and take that as well. With the double pressure from knights, you can sneak the Grave Golem incredibly easy with three people. It can be two manned as well, but this takes significantly longer. With such overwhelming map pressure from your mercenary camps, you should have essentially uncontested turn in. Keep your eyes on the scoreboard constantly to be aware of the doubloons the enemy team has. If there is a single member with several coins, try to catch them by hiding in the fog of war near turn in. This map snowballs harder than any other, so constantly be contesting turn in when ahead to cement your victory.