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 level up 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. Keep in mind that by level 2 no difference is made and by three the choice is yours meaning that Sacrifice to Frost Blast to Frost Blast puts you level at Level 3, whereas Frost Blast to Sacrifice to Frost Blast gives you virtually no advantage.
 * Try using Sacrifice on friendly creeps as they travel towards your lane, when done properly you can Sacrifice the creep within your and your lanepartner's XP range, but outside of the XP range of your enemy, when done consistently an enormous level advantage can be obtained. This is especially important to do in lanes with powerful ultimates. For instance, when laning with a Viper against a Riki, getting Viper to level 6 before Riki can net you a kill, whereas Riki getting to level 6 before Viper will require you to get detection for that very same kill attempt.
 * 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.
 * Although unmentioned a Refresher Orb can also be a viable pick on Lich which increases his ultimate ability's damage output by a very large margin, especially if it is a follow up on disabling team fight abilities such as Tidehunter's Ravage, Faceless Void's Chronosphere and Magnus' Reverse Polarity.

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: the first is an alternate to "OM NOM NOM", used when the Sandvich Edible Device is consumed.
 * Lich is almost a copy of the Warcraft 3 Lich hero, who can learn Frost Nova, Frost Armor and Dark Ritual; in Dota 2, these skills were renamed to Frost Blast, Ice Armor and Sacrifice, respectively.
 * 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.
 * In an earlier version of DotA, Lich and Crystal Maiden shared the same Frost Nova ability. In later versions, Crystal Maiden's skill was  changed into a target-area slow called Crystal Nova, while Lich kept the original version.
 * Anatomically, Lich's cranium have no visible sutures, so that is another proof of his oldness.