After a month and a half dry spell following the release of Elder Titan, Valve has added another hero to DOTA 2 within a week of the game's release from beta. While Legion Commander seemed a likely candidate for the next hero to make the cut (based on textures and other materials found in the game files), shadow-clad Abaddon, the Lord of Avernus, made the cut first.
As you might gather from his character design, Abaddon's lore casts him in a decidedly sinister light:
The Font of Avernus is the source of a family's strength, a crack in primal stones from which vapors of prophetic power have issued for generations. Each newborn of the cavernous House Avernus is bathed in the black mist, and by this baptism they are given an innate connection to the mystic energies of the land. They grow up believing themselves fierce protectors of their lineal traditions, the customs of the realm--but what they really are protecting is the Font itself. And the motives of the mist are unclear.
When the infant Abaddon was bathed in the Font, they say something went awry. In the child's eyes there flared a light of comprehension that startled all present and set the sacerdotes to whispering. He was raised with every expectation of following the path all scions of Avernus took--to train in war, that in times of need he might lead the family's army in defense of the ancestral lands. But Abaddon was always one apart. Where others trained with weapons, he bent himself to meditation in the presence of the mist. He drank deep from the vapors that welled from the Font, learning to blend his spirit with the potency that flowed from far beneath the House; he became a creature of the black mist. There was bitterness within the House Avernus--elders and young alike accusing him of neglecting his responsibilities. But all such accusations stopped when Abaddon rode into battle, and they saw how the powers of the mist had given him mastery over life and death beyond those of any lord the House had ever known.
With Abaddon's release, here's what you need to know once you start playing him or encountering him in the queue.
In some ways, Abaddon can be compared to supports like Dazzle and Omniknight, though neither is a perfect analogue. While his skill set lends itself well to support, he could fill a wide variety of roles, with both offensive and defensive potential. His abilities make him very tanky, key for a melee hero, but he can also enhance his entire team's sustain and counter enemy debuffs. His Aphotic Shield both buffs his team's survivability and their damage output, and by packing a heal, a team-buff-on-hit ability, and an ultimate that dramatically increases his own tanking power, Abaddon enables sudden, dramatic turnarounds in hectic teamfights.
Mist Coil (formerly Death Coil) is a dual-purpose heal/nuke that deals self-damage to Abaddon when used. It has good range (slightly longer than Omniknight's Purification, slightly shorter than Dazzle's Shadow Wave) and deals 100/150/200/250 magical damage to its target. Abaddon suffers half the damage dealt as pure damage. Mist Coil has a low cooldown - only 5 seconds - and costs a reasonable 75 mana. It can also be used by Abaddon to deny himself, although since Mist Coil cannot be self-cast, you'll need to be within range of an ally or enemy you can target.
Aphotic Shield is Abaddon's most important skill. Slows, stuns, silences - cast an Aphotic Shield on someone and all those nasty effects just slide right off. Even Batrider's Lasso is broken by it, something that might make waves in the competitive metagame. But removing debuffs is only half the story with Aphotic Shield. The other half is that the shield absorbs a set amount of damage (110/140/170/200), and once its cap is reached, explodes to deal that damage to anyone within 650 units. In a team fight, that can be a real game changer. It's easy to see a bevy of uses for Aphotic Shield - tower dives, turning team fights around in the space of a few seconds, setting up ganks and ensuring your bait survives to boot. When maxed, Aphotic Shield has a 6 second cooldown, and combined with its 15 second duration you can send you team into battle with two Shields up at once. Not too shabby!
Curse of Avernus, which in the original DOTA was named for the iconic Warcraft III sword Frostmourne, activates upon hitting an enemy. Enemies struck by Abaddon are slowed for 2.5 seconds by 5%/10%/15%/20%. Further, any allies who hit the same target are buffed with increased movement speed and attack speed for 4.5 seconds. Curse of Avernus is something of a one-point wonder; if your playstyle relies on facilitating early game ganks, it can be a great help for keeping your team in range of a target and bringing them down quickly. Curse of Avernus also applies to towers, allowing Abaddon to help any pushing-focused lineups and get that sweet, sweet tower gold.
Lastly, Borrowed Time, Abaddon's ultimate, is yet another tool of reversal, this time by purging negative buffs and temporarily turning any damage Abaddon takes into heals. Borrowed Time can be manually triggered, for no mana and a reasonable 60/50/40 second cooldown, but also triggers automatically when Abaddon drops below 400 HP. The source of damage need not matter - Abaddon's Mist Coil damage will heal him while Borrowed Time is active, so spread the love. Borrowed Time doesn't heal HP loss (so Armlet of Mordiggian and Soul Ring will still drain his health like normal), and can still be countered by Axe's Culling Blade. Massive burst damage can also kill Abaddon outright before Borrowed Time automatically triggers (for example, Laguna Blade dropping Abaddon from 401 HP to 0 HP), though careful timing would need to be used and a quick player could still manually trigger the ability.
While it's active, however, Abaddon can be damnably hard to kill. With Aghanim's Scepter, the duration of Borrowed Time increases by two seconds per level (3/4/5 to 5/6/7), so if you're the party tank or you're flush with cash, it's worth considering. While living on Borrowed Time, try to cause havoc; make the most of your low cooldown abilities and get some hits in with Curse of Avernus.
Abaddon has already made his mark on DOTA 2 by unseating Alchemist from the default hero position at the front of the alphabet. A Captain's Mode implementation can't be ruled out before The International 2013, but it seems rather unlikely with less than a month to go before the big event.