Outworld Destroyer

Harbinger the Outworld Destroyer is the sole Intelligence hero who qualifies as a Hard Carry. His damage output is entirely reliant on his Intelligence stat and the size of his mana pool, so he must focus more or less exclusively on items which augment them. Though extremely fragile (rendered even more so by his inability to build any significant durability items), he deals Pure damage which increases with his mana pool, meaning that if he gains an advantage in a match he deals constant, colossal damage which (because it is Pure damage) cannot be decreased or resisted. He and his allies enjoy more-or-less unlimited mana because of his aura, he can protect himself or an ally, or disable (and steal Intelligence from) an enemy, and he can instantly deal colossal area damage with his ultimate. Because of his ability to constantly and limitlessly replenish his mana, he is arguably the only hero in the game who directly counters Anti-Mage.

Tips

 * One of Harbinger's biggest weaknesses is his fragility. Avoid taking in too much damage; if so, you will miss out on potential gold and experience, as well as put your team in danger by not dealing the needed extra damage against your enemies. Try to fight in the sidelines, or when your enemies are too busy to attack you. If you wish to boost his health through items, try to include additional Intelligence with it; if not, make sure the item gives him the health boost that makes him take more damage.
 * Try to level up as much as possible in the early stages of the game, be it from farming or killing other heroes. The more you advance in level, the more Intelligence and gold you will receive. The more Intelligence and gold you receive, the better you will dominate in the battle.
 * Level up Harbinger's Essence Aura as soon as possible so that he can quickly solve his mana problems right away. Essence Aura can also make a good support skill for your allies, especially if they rely heavily on casting spells.
 * Astral Imprisonment is Harbinger's disabling skill, and can be used in numerous ways:
 * Early in the game, it can be used to harass against heroes you are laning against.
 * Strength and Agility heroes are ideal targets, since Astral Imprisonment steals Intelligence from their already low supply. They can repeatedly be disabled to the point that they are unable to cast spells (the steal stacks up to five times, stealing a total of 20/30/40/50 Intelligence).
 * Intelligence heroes lose damage as well as have their mana pool lowered, while Harbinger increases his.
 * Astral Imprisonment can be used to delay enemy heroes you are laning against, giving you more time to either deny or last-hit creeps.
 * Astral Imprisonment can be used to dodge incoming spells when cast on yourself or allies; spells like Tinker's Heat-Seeking Missile, Sand King's Epicenter, or Sven's Storm Hammer can be rendered useless when under Astral Imprisonment.
 * Astral Imprisonment can also be used to buy time, be it escaping or trying to chase an enemy. While escaping, you can cast it on yourself or any dying ally to shift the enemy's focus away. While chasing, you can step ahead of the imprisoned enemy's path and make it harder for them to escape.
 * Use Astral Imprisonment carefully against your enemies when your allies are present in the team fight. Using it too much in these situations can potentially block your allies' skills, especially if they are channeling disables (i.e. Pudge's Dismember). Use it when your teammates are out of disables, or when the enemies are in the process of escaping. As well, try to target other units that are currently not disabled or crippled by your teammates.
 * Because of its utility, versatility, and Intelligence steal, Arcane Orb is usually taken first before most other skills.
 * When Harbinger's Essence Aura is high enough (at least Level 3), you can keep casting Arcane Orb against enemy targets to restore his mana right away if depleted.
 * Casting Sanity's Eclipse can prove important when a team fight starts, since it can shut down spell-reliant casters by burning 75% of their mana, as well as soften Strength and Agility heroes. Keep in mind that your Intelligence must be marginally higher than theirs so that these effects can work.
 * Outworld Destroyer has no reliable escape until he gets force staff. Frequent early ganks can put him at a severe disadvantage.

Hero Tips

 * Other Intelligence heroes, most notably Silencer, can render Sanity's Eclipse useless. Make sure you have at least affected their allies, and be prepared to engage them in other means.
 * Pugna's Nether Ward will count Arcane Orb as a spell cast, so make sure to destroy it before liberally using Arcane Orb against other enemy heroes.
 * Arcane Orb deals bonus damage against illusions, making it harder for illusion-reliant heroes like Phantom Lancer or Chaos Knight to fight you. Summoned units also take additional damage, turning units like Enigma's eidolons and Nature's Prophet's treants into easy gold.
 * Outworld Destroyer counters Anti-Mage, since he can regain mana instantly from Essence Aura just by auto-casting with Arcane Orb. In these battles, make sure to max out Essence Aura first.

Trivia

 * Outworld Destroyer was originally called Obsidian Destroyer in the first Dota. Obsidian Destroyer was based off of two units in Warcraft III: Frozen Throne; the Obsidian Statue, and its flying version, the Destroyer.