Lich

Ethreain the Lich is a ranged intelligence Hero that uses his abilities to slow his enemies down with his ice-based attacks, as well as giving a boost to ally defenses, and serves as a great teamfight ganker with his powerful ultimate. He can use Sacrifice to easily deny creeps and keep his mana high, making him very good at harassing in the early stages of the game. While a relatively frail hero and mostly known as a support, he can prove to be a force to be reckoned and mighty foe to stand with as he can render the attempts of multiple enemies futile with his ultimate, Chain Frost. Lich is a powerful crowd controller and can easily turn a teamfight, or dominate in a lane.

Tips

 * Spamming Frost Blast and Sacrifice early game can be extremely effective by harassing and denying efficiently.
 * An effective strategy is to take Sacrifice immediately. Even though you won't need the mana earned from it, you can deny a creep immediately to prevent the enemy from earning experience and to pull the lane towards your tower.
 * A Refresher Orb is a great item to purchase as it allows him to cast his Chain Frost twice in a battle, coupled up with Aghanim's Scepter and Veil of Discord, Lich can be one of the most destructive damage dealers in team fights.
 * Despite primarily being a support hero, Lich can play a very effective mid. Combining his powerful Frost Blast to harass the enemy while denying his own creeps can shut down the enemy's laning phase.
 * Ice Armor is a very cheap yet effective ability. Cast it on nearby allies to keep their armor up, or yourself to increase your own survival.
 * Keep in mind that Ice Armor can be set to auto-cast, automatically casting it on heroes that are being attacked.
 * Since Lich already has high armor thanks to his Ice Armor, getting a Cloak or even Hood of Defiance will greatly improve his survivability. It can also be built into Pipe of Insight later.
 * Chain Frost can be one of the most devastating ultimates in the game, and can easily turn a teamfight in your favor when used properly. Each time it hits, it deals very high magic damage and bounces to another random enemy unless there are no targets nearby. Use it to deal damage quickly to clustered Heroes.
 * One of the biggest disadvantage of Chain Frost is its slow movement speed. This gives time for enemies to split apart preventing chain frost from bouncing. You can however, work with heroes like Dark Seer's Vacuum, Faceless Void's Chronosphere or Enigma's Black Hole which locks heroes in place taking the full damage from Chain Frost for an extremely devastating damage.
 * Heroes like Queen of Pain, Death Prophet or Tiny are able to clear creep waves quickly allowing Chain Frost to deal its full damage to heroes.
 * When casting Chain Frost on a lone Hero (targeting the hero with chain frost) with 5 creeps, there is approximately ~55% chance of it hitting a hero twice, and ~65% of it hitting a hero twice with 3 creeps. This almost assures a kill on most lone heroes provided the enemy has no escape mechanism with 3 creeps at early levels. Be sure to follow up with a Frost Blast to slow them from escaping Chain Frost range.
 * If Lich catches the enemy team killing Roshan, using Chain Frost will force them to desist and/or deal huge damage to all of them; as Roshan's Lair is very difficult to disperse inside, especially when slowed.

Trivia

 * Lich's voice actor, Gary Schwartz, also voiced the Heavy and Demoman classes in Team Fortress 2, another title by Valve. Lich's lines, "UM NUM NUM" refer to a line said by the Heavy class in Team Fortress 2: the first is an alternate to "OM NOM NOM", used when the Sandvich Edible Device is consumed.
 * In the transition from DotA to Dota 2, three of Lich's skills have had their name changed. Frost Blast used to be called Frost Nova, Ice Armor used to be called Frost Armor and Sacrifice used to be called Dark Ritual.
 * In the first iteration of Invoker's skill build, when the order of his three orbs determined the spell that was invoked, Frost Nova was one of his abilities and functioned almost identically to the current spell, and was mapped to Quas Quas Exort.
 * In DotA, Lich was known as Kel'Thuzad, a notable character from the Warcraft universe.