Anti-Mage is an extremely hard carry who starts off very weak in the early game but becames very powerful in the late-mid to early-late game. Anti-Mage is very powerful because he becomes effective extremely quickly, while still being an unstoppable beast.
The monks of Turstarkuri watched the rugged valleys below their mountain monastery as wave after wave of invaders swept through the lower kingdoms. Ascetic and pragmatic, in their remote monastic eyrie they remained aloof from mundane strife, wrapped in meditation that knew no gods or elements of magic. Then came the Legion of the Dead God, crusaders with a sinister mandate to replace all local worship with their Unliving Lord's poisonous nihilosophy. From a landscape that had known nothing but blood and battle for a thousand years, they tore the souls and bones of countless fallen legions and pitched them against Turstarkuri. The monastery stood scarcely a fortnight against the assault, and the few monks who bothered to surface from their meditations believed the invaders were but demonic visions sent to distract them from meditation. They died where they sat on their silken cushions. Only one youth survived--a pilgrim who had come as an acolyte, seeking wisdom, but had yet to be admitted to the monastery. He watched in horror as the monks to whom he had served tea and nettles were first slaughtered, then raised to join the ranks of the Dead God's priesthood. With nothing but a few of Turstarkuri's prized dogmatic scrolls, he crept away to the comparative safety of other lands, swearing to obliterate not only the Dead God's magic users--but to put an end to magic altogether.
-A lot of extra static damage from Mana Break
-The best escape mechanism in the game, Blink
-A super-effective magic resistance SHield, Spell Shield
-Can be effective much earlier than other carries
-Mobility allows extreme farming the jungle
-Extremely squishy through most of early to mid game
-Extremely vulnerable to ganks with silences and disables
-Requires a lot of farm to be effective
Anti-Mage's first ability is a passive called Mana Break. Mana break will add a mana burn with each hit Anti-Mage makes, starting with 28 mana burned and going up by 12 until it maxes out at 64. Mana Break will also give 60% extra damage for each point of mana burned. It is a unique attack modifier, which means it will not stack with most other attack modifiers such as Mask of Madness or Diffusal Blade. A Black King will block both the damage and mana burn of Mana Break.
Mana Burn: 28/40/52/64
Anti-Mage's second abilitly is Blink, short distance teleportation. It is the best escape skill in the game and is a great chasing skill as well. With a low mana cost and short cooldown, Blink will allow Anti-Mage to survive most ganks and chase down enemie with impunity.
Mana Cost: 60
Anti-Mage's third ability is a passive called Spell Shield. Spell shield gives Anti-Mage magic resistance. When maxed out it will give Anti-Mage a 62.5% magic resistance shield (because of natural 25% magic resistance). Spell shield allowes Anti-Mage to shurg off high-damage nukes such as Finger of Death or Zeus' Thundergod's Wrath.
Anti-Mage's ultimate ability is Mana Void. Mana Void will deal damage based on mana missing, which means it fits perfectly with his first ability that burns mana. It is usually used to finish off fleeing opponents but can be used to great effect if cast correctly in teamfights, as it applies the damage dealt in a large AoE, which can result in surprising multi-kills if used on opponents with a depleted mana pool. It is also useful for canceling channeling abilities such as Keeper of the Light's Illuminate or a teleportation.
Damage dealt per mana point missing: .6/.85/1.1
Stun Duration: .1/.2/.3
Mana Cost: 125/200/275
At the beginning of the game, the best skill point is Blink. Blink will allow you to escape ganks and dodge spells, and will give Anti-Mage a lot better survivability.
The second point is Mana Break. An extra point into Blink does not help much. It reduces cooldown by 3 seconds and increases the range slightly. You should not be spamming Blink early on in the first place so the decreased cooldown does not help much and the increased range is so slight to be almost unnoticable. Mana Break allow Anti-Mage to do some minor harassment while laning. Always take an opportunity to hit an opponent and burn their mana.
The third point should almost always be invested in Spell Shield unless the other team has no spellcasters. Which is impossible. 1 point in Spell Shield gives 26% magic resistance for one point.
After this, the build may alter slightly. Most players choose to grab two stat points to gain a little bit of health to increase their survivability. If you are facing heroes with high physical damage such as Drow Ranger or Sniper, it may be wise to grab a few stat points. However, if you are facing a nuker such as Zeus or Queen of Pain, it may be wise to grab a few points of Spell Shield to give yourself some survivability against them.
However, if you are getting ganked by heroes such as Night Stalker or Pudge, it would be wise to get a few points of Blink so you can always escape. Even one second for Anti-Mage is enough for him to escape but only of his Blink is off of cooldown.
The hardest part of an Anti-Mage game is laning. While Anti-Mage has a decent amount of starting strength, his strength gain is quite pitiful at +1.2. This will lead to you having much less HP than many other heroes in the game. Because of this, Anti-Mage will require a Stout Shield for a little damage block as well as a tango and healing salve to keep him at max HP. It would also be wise to pick up 3 Iron Branches to give a little more health as well. The three branches can easily be upgraded into a Magic Wand later in the game.
If you are facing a lot of trouble in lane, pick up a Magic Wand using your three branches. It will provide you with a lot of burst HP and will also help against heroes who spam their spells ( Zeus, Phantom Assassin). If you are facing even more harass, pick up a Poor Man's Shield or even a Vanguard. While buying these survivability items may slow down your build, if they save your life even once, it is worth it.
If you are comfortable with the amount of harass in lane, immediately buy either Boots of Speed or Ring of Health. I prefer to buy a Ring of Health first, while others would rather get Boots. It is entirely up to you. However, you should have a Ring of Health and Power Treads by the time you finish the early laning phase.
During laning, NEVER NEVER NEVER tower dive to get a kill. One kill is not worth one death. Unless they're down to less than 100 health never try to get a kill under a tower.
Also, try to hit the enemy as much as possible during laning. Safely, of course. Each hit translates to mana burned and will help a great deal with heroes with low mana pools and mana-draining such as Clinkz or Drow Ranger.
Now that the early laning phase is finished, you should start working on your Battlefury. A Battlefury is a core item on Anti-Mage because it gives so much farming potential with Blink. An Anti-Mage with Blink and a Battlefury can flash-farm the jungle in 45 seconds and repeat in an endless loop. A Battlefury will also allow you to push your creep lane extremely easily as you can kill creeps very fast. A common strategy is to Blink well far ahead of your creeps and clear out an entire enemy creep wave, allowing the creeps to pressure by themselves.
After a Battlefury, Anti-Mage should leave the lane for the jungle. At this point, you are still extremely weak and should not join in teamfights. If your team is overwhelmingly destroying the other team, feel free to Blink in and use Mana Void to steal kills. As an Anti-Mage any kills towards you, rather than to, say a Pudge or Bloodseeker will be better for the team.
One should start to acquire a Manta Style in the jungle. A Manta Style complements Anti-Mage extremely well, as your illusions will also get Mana Break. With a Manta, Anti-Mage will be able to burn 192 mana per hit, since all three illusions are hitting for 64 mana burn. The illusions will also gain the bonus 38 damage, leading to massive amounts of damage being dealt. A Manta will also give much needed movement speed thanks to Yasha as well as massive amounts of bonus Agility. It will also allow you to Manta-dodge, or use the Manta Style a split second before a projectile hits. That will block the damage since using the Manta renders you invulnerable for 0.1 seconds. Using the Manta will also remove any negative debuffs such as Desolator's Corruption.
Once you have your Manta, feel free to jump into teamfights. With illusions you should be doing massive Mana Break and damage and you should be able to solo most heroes. Of course, still be careful and do not initiate! You are still very squishy and if you initiate with Blink there is a high chance of being bursted down. Let the other team initiate or some other hero initiate. Always save your Blink for escaping. One death could ruin everything.
Once you have your Manta, you have several options to work for. The first and most obvious choice is a Vladimir's Offering. As an aura, it will stack with Mana Break, and the extra armor aura is very tempting. However, Vlads do not scale very well and become fairly useless in the late game. I personally do not ever go Vlads.
Another option is to go for a Heart of Tar***que. A Heart will give you an astounding 1060 health points and give you incredible regeneration. On an Anti-Mage a Heart will put your regeneration to around 62 and that number will go up. With a Heart Anti-Mage can and should tank infinite creep and tower damage. Of course, the incredible regeneration does not work when under hero fire, but the extra 1060 health will still be a great asset in a fight.
After a Heart, one can go after a Butterfly. A Butterfly will give you attack speed, damage, agility, and evasion, all in massive amounts. Great? Not really if the other team has a Monkey King Bar. An MKB will completely shut down a Butterfly's evasion, which is the best feature of a Butterfly. With an MKB, a Butterfly is still worth it. It will provide massive amounts of DPS and will force an MKB from the other team.
Another option after Heart is a Skull Basher. It will provide a bash chance of 25% for 1.4 seconds. It will also add damage and strength, and can be upgraded later to an Abyssal Blade. I would personally get a Skull Basher first because it is much cheaper, and is still very effective. Of course, get both if possible.
At this point you can just be walking around the map killing random towers and heores. It may not be practical but it sure as hell is fun. M-m-m-m-m-monster kill!
If an Anti-Mage has reached all his Core Items, he will no doubt be destroying the other team. At this point, one should aim for Luxury Items.
The first Luxury Item is an Abyssal Blade. Upgrading from a Skukll Basher to an Abyssal is quite expensive- a Sacred Relic is 3800 gold with no assemble. However, it will give you a 2 second stun that goes through magic immunity as well as an extra 100 damage and 10 strength. It is well worth the cost.
The second Luxury Item is Boots of Travel. It will give Anti-Mage extreme mobility as well as a lot of extra movement speed. By now the +8 agility from Power Treads will be almost useless, so it is always a good idea to trade Treads for BoT. Also remember to disassemble the Treads and use the boots instead of selling and buying boots again.
The third Luxury Item is a Divine Rapier. With +300 physical damage, the Rapier is the most cost-efficient damage item in the game. Replacing your Battlefury with a Rapier will greatly increase your DPS. Of course, be careful not to die, or the Rapier will be lost. Also never buy more than one Rapier unless you can afford six.
Here's Purge, a very good Dota 2 player playing Anti-Mage.