Lina

Lina the Slayer is a ranged intelligence hero, adept at destroying enemy heroes fast and delivering massive bursts of magical damage, making her one of the most effective early gankers. Her spell damage diminishes as the game goes on; but her basic attack power grows and her passive ability allows her to use it to great effect. Her stun, when mastered, is a boon to her team; and even into late game she remains extremely skilled at assassinating single targets (hence 'the Slayer'). In a large encounter, Lina is best used by using her powerful nukes to annihilate the more frail enemy units, then turning her fiery gaze onto the remainder with hyper-accelerated attack speed.

Tips

 * Combining Light Strike Array with a guaranteed stun such as Vengeful Spirit's Magic Missile or Sven's Storm Hammer makes Lina a serious ganking force early on.
 * Positional items such as Blink Dagger, Force Staff or Phase Boots can help you a lot landing Light Strike Array and thus your whole spell combo without relying on other heroes.
 * Always cancel the backswing animation after casting your spells, especially when you plan to skill Fiery Soul.
 * In teamfights it can be very beneficial to quickly focus on low hp or support heroes, as Lina has very good nuking abilities.
 * Laguna Blade should not be used as a finishing blow, since that can waste most of the spell's massive damage. It is best used to cripple enemy carries or obliterate their supports; but using it when its damage far exceeds the target's remaining HP is a waste. There is a temptation to use it on fleeing heroes as it is the only one of Lina's abilities that is long range and target-unit; but it is wiser to build Blink Dagger instead to avoid having to expend it. That said, with the latest update as of 6.75b parity, the much reduced cooldown means that usage of Laguna Blade should be far less sparing, with mana cost the only remaining issue.
 * When paired with Pugna or Shadow Demon, both of whom have percentage-based damage-increasing mechanics; Lina's burst damage becomes gigantic (a sceptred level 3 Laguna Blade will do about two thousand damage alone) to the extent where she can assassinate enemy heroes with a significant gear/level advantage over her.
 * Lina is more or less exclusively a nuker, and in a typical late-game encounter she is most wisely utilised via staying away from the fray and using her Dragon Slave and Light Strike Array effectively; saving her Laguna Blade for a crucial moment.
 * If the role of suppport/disabler is covered and Lina has the basic items she needs; she benefits greatly in late-game from building items that augment the power and utility of her basic attack; as while her nukes lose potential as the game goes on, Fiery Soul ensures she has a scaling ability to make her presence felt. Some basic items for this build are Daedalus, Eye of Skadi and Monkey King Bar.
 * Lina's Laguna Blade can hit for around 2500 damage if she combines Aghanim's Scepter and Refresher Orb, granting her enormous nuking power.
 * If Lina is tending to be targeted first (this is a very common tendency), some tanky/utility items will be of great use.

Trivia

 * The original Lina Inverse "The Slayer" was modeled after the main character from the novels/anime/manga Slayers who went by the same name. Her Dragon Slave and Laguna Blade are both spells used by the original Lina Inverse.
 * Lina was the first hero to be made in Dota 2.