Slark

Slark the Nightcrawler is a melee agility hero that utilises his skills to spring onto enemy heroes and slip out unhindered. He is a very mobile ganker, but remains statwise below most other carries unless he is able to steal away attributes with his abilities. Once he does, though, only a few heroes can hope to be as fearsome as the Nightcrawler - extremely mobile to the point of ever-presence; his strikes only hitting harder and faster.

Slark can quickly leap forward onto enemies with Pounce to leash them and bind them from escaping. His Dark Pact releases a delayed purge that breaks even the most powerful disables. This gives him one of the most flexible abilities to start and end fights in the game. He is also capable of stealing attributes on auto-attacks to boost his own damage temporarily with Essence Shift which can rapidly shift engagements in his favor, even when merely performing hit-and-run maneuvers. Slark's ultimate, Shadow Dance, allows him to remain unseen even while attacking for a short duration and allows him to move quicker when not under the watch of enemy eyes to strike in and out of enemy ranks unhindered.

Tips

 * Slark is most often played as a Mid hero, as Midlane maximizes his Ganking potential early, assuring he will become dominant by late game. However, Slark is fairly unique in that he can excel in every lane, if up against the right heroes, and can even be played as a solo offlaner thanks to Pounce.
 * Pounce is good for both chasing and escaping enemies. It can be used like a blink dagger to jump into, from, or through otherwise impassable terrain to great effect.
 * Dark Pact is a wonderful tool for purging the negative debuffs placed on him. When used at the right time, during the delay, the waves emitted from Slark will also remove the incoming debuffs about to be placed on him, allowing you to "dodge" or shorten their duration.
 * Unlike most purges, Dark Pact can purge stuns from Slark - bear this in mind if you have been targeted by a slow moving projectile stun (such as Sven's Storm Hammer or Alchemist's Unstable Concoction) and time your activation of Dark Pact to remove it as it strikes. With enough practice you can time it to almost completely nullify their usage.
 * Dark Pact also offers Slark a very interesting kind of advantage against certain defenses. The burst from Dark Pact is calculated as 10 attacks very quickly after another, meaning that Slark can use it against buffs like Living Armor, which offer protection but only defend against a set number of damage instances before disappearing.
 * Dark Pact is a great way to finish off an invisible unit that has been leashed, as the AOE damage effects invisible prey.
 * When being chased, try to get out of sight from the enemy, be it around trees, up hills, et cetera. The passive from Slark's ultimate will activate when out of enemy sight and give you a boost to move speed and HP regen for a short moment before sight is regained. This can be the difference between life and death.
 * If timed right, Pounce can be used to dodge some projectile skills such as Sniper's ultimate, as Slark is invulnerable during his jump (note that some disables can catch Slark mid-air, though no damage will be dealt).
 * A helpful side effect of Shadow Dance's passive is that Slark gains a weak form of detection. If you find that you've suddenly lost your movement speed and health regeneration bonuses while seemingly alone, it means one of three things. First, it can mean enemies are lurking around in the area that you can't see and you should be extra cautious- a gank may be incoming. Otherwise, if your enemies are all accounted for, it means the enemy has wards in the area, and you should let your team know this so they can react accordingly, or deward. Lastly, if Bloodseeker has skilled his Thirst, Slarks ultimate will be disabled while he is below half health, while revealing Slark's location to his foes. This makes Bloodseeker one of the most effective counters to Slark in the game.
 * Slark functions a bit differently from most carries - while a standard carry capitalizes on sustained damage, Slark can take on more of a hit-and-run approach. You can maximize his Essence Shift's duration by continually harassing and retreating. Go for the kill once you think you have enough damage and attack speed to take down enemy heroes. Slark's base attributes are average at best, although with enough stolen Agility and damage items he can keep up with hard carries such as Phantom Assassin and Sniper.
 * Maximize Essence Shift's efficiency by taking objectives using his stolen attributes. After a large teamfight, it is not uncommon to find that Slark has stolen upwards of 50 agility, making quick work of untended towers or Roshan.
 * Vladmir's Offering is a great item on Slark for multiple reasons. First, it gives you much needed armour and mana regen. Second it gives you lifesteal and a small amount of HP regen, which is great for the survivability of a squishy ganking hero like Slark. Most importantly, however, is the 15% boost to your base damage which, due to Essence Shift, is constantly increasing with each attack that Slark makes on an opponent. This drastically increases the effectiveness of Essence Shift over time.
 * Soul Ring provides a cheap source of instant mana, as Shadow Dance can easily regenerate the health cost when out of battle
 * If played as a midlane hero however, a Bottle can be a much better choice, healing you in combat situations and giving you mana when needed. Slark's passive speed boost from Shadow Dance also means he can out rune control most midlane heroes easily.
 * Orchid Malevolence offers all the mana regeneration you will ever need, bonus attack damage and speed, as well as the damage amplifying Silence ability. Together with Pounce, it will lock down any target almost completely. Note, however, that this item choice does not supplement your naturally low health at all. Orchid Malevolence is most useful against intelligence heroes that can easily burst-damage you down, such as Lina, and heroes that can escape from Pounce's leash, such as Anti-Mage and Queen of Pain.
 * Against Physical Damage dealers, such as Phantom Assassin for example, a Ghost Scepter works extremely well on Slark. Ghost Scepter gives you an added escape mechanism early along with much needed stats, and builds into Ethereal Blade.
 * Ethereal Blade gives Slark a huge damage and attack speed boost, Some HP, Armour and Mana, and yet another nuke and slow that synergizes well with Slarks skill set. This is due to Ethereal Blade's nuke damage coming from how much agility Slark has, and thanks to Essence Shift this can be an absolutely devastating amount of damage, especially if followed up by a Pounce and Dark Pact. Note that Ethereal debuffed units take 40% additional magic damage, boosting the damage output from both of your other nukes. One might think this is counter intuitive, as Dark Pact deals self damage, However Dark Pact will purge the ethereal debuff from Slark before taking approximately 95% of the self damage. If used correctly, Slark can use Ethereal Blade, time his Pounce and Dark Pact so that Slark can do full extra magic damage to the ethereal unit, Purge the ethereal debuff from Slark, and then be able to physically attack the leashed unit for an almost guaranteed kill. Ethereal Blade's Active can also be used to catch up to and/or finish off fleeing foes that are out of Slark's reach, as the nuke has a very long cast range.
 * Skull Basher Serves as a dual purpose item for Slark, Giving him a passive bash and a huge damage boost, while also providing some HP. Late game Skull Basher can be upgraded into an Abyssal Blade for even more damage and HP and a guaranteed stun that goes through magic immunity.
 * A good alternative for a Unique Attack Modifier (albeit a less defensive one) would be the Diffusal Blade. While it may not provide him the same survivability as the Eye of Skadi, it grants excellent Agility attribute boosts, 8/16 (Lv1/Lv2) total uses of the Purge active, and the signature manaburn attack modifier, which is a good countermeasure against spell-dependent foes.

Trivia

 * The DotA version of Slark bears many similarities with a rare World of Warcraft creature of the same name.
 * Slark's murloc heritage was completely removed in transition to Dota 2 to avoid copyright issues, since the murloc are an existing race in the Warcraft universe.
 * Slark's response upon activating a Double Damage rune, "Met you once, cut you twice," may be a reference to the phrase "Measure twice, cut once"
 * Slark's response upon respawning "Griefer madness" may be a reference to one of the worst films in cinema, Reefer Madness.