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 experience and stats with his abilities, which he can do often, and then may become a hunter that is even more feared and more ubiquitous.

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 among the most flexible ability to start and end fights in the game. He is also capable of stealing stats 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 manuevers. 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

 * If you are low on HP after level 6, try to avoid being attacked and then take advantage of your ultimate's passive healing ability.
 * When being chased, try to get out of sight from the enemy. The increased move speed from Slark's ultimate will allow for easy escaping.
 * Try to take advantage of the bonus attack speed from both Mask of Madness and Essence Shift but be wary of the increased damage taken as Slark is very squishy.
 * Dark Pact can purge debuffs such as Slardar's Amplify Damage, Dust of Appearance and Bounty Hunter's Track.
 * Gem of True Sight, Lvl 3 Necronomicon and Sentry wards are arguably the best counters to an invisible Slark.
 * Pounce is good for both chasing and escaping enemies.
 * 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 is 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.
 * Your invisibility gives off a smoke visual that will alert enemies that you are present, but they can't see you. This could be a big drawback to Slark's potential, as there's a chance that he will be revealed. Be wary and cautious when facing heroes, especially those with Dust (although it is purgable by Dark Pact), Gem of True Sight and a Lvl 3 Necronomicon.
 * Slark functions a bit differently from other carries - while other carries capitalize on sustained damage, Slark takes on a more hit-and-run approach. Abuse 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 stats are average at best, although with enough stolen Agility he can keep up with hard carries such as Phantom Assassin and Sniper.
 * Maximize Essence Shift's efficiency by taking objectives using his stolen stats. 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.
 * There are two main skill builds for Slark: one of them is based on maxing Dark Pact after maxing Pounce, with one point in Essence Shift; this way, you'll have a good nuke with a very low cooldown, which works perfectly with your Pounce. The second build is based on his passive ability, Essence Shift: the more you attack enemy Heroes, the stronger you'll get, since you'll gain more and more agility.
 * While not mentioned in the default build, Shadow Blade makes a great addition to his skill set for both set-up and escape from ganks. The twelve second invisibility also provides a means of hp regen after taking damage from team fights without being forced to leave the area. Allowing you to mop up any retreating heroes for some extra gold and exp.
 * If timed right Pounce can be used to dodge some projectile skills such as Sniper's ult.

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, along with Enchantress,  Meepo and  Luna (with Lunar Blessing), is one of the few heroes to have 1800 sight range at both day and night.
 * Slark's response upon activating a Double Damage rune, "Met you once, cut you twice," may be a reference to the popular Design Technology phrase "Measure twice, cut once"