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. Though her fiery power decreases in the later stages, her spell damage is nevertheless still powerful enough to kill a single hero. Everytime she casts a spell, her speed, both attack and movement is enhanced to a higher level, allowing her to inflict more damage using her normal attacks.

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 sufficiently farmed in mid game with ideally a Blink Dagger and an Arcane Boots at least, it is possible to build her almost as an hard carry with Bloodstone, Phase Boots, Ethereal Blade, and any other 2 damage/AS boosting items like Daedalus, Yasha or the like. Eye of Skadi is suitable due to the massive slows but does not provide bonus damage, so may not be so suitable.

Trivia

 * The original Lina Inverse "The Slayer" was modeled after the main character from the anime/manga Slayers.
 * Lina was the first hero to be made in Dota 2.