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 gankers in the game. She possesses immense damaging capabilities all throughout the game, but is very fragile. Two of her fiery spells are her main source of damage, Dragon Slave sends a wave of fire to burn enemies in her path while Light Strike Array stuns them with a concentrated pillar of solar flame. Each of her spells deals great damage early on and has a low cooldown. Her Fiery Soul bolsters her attack and movement speed exponentially every time she casts a spell, which gives her scaling damage for the later game. Laguna Blade, her ultimate, is her ace in the hole. Lina fires off a huge bolt of lightning at a single target, dealing colossal damage. Laguna Blade's damage is staggering in early-mid game, and late game is still enough to destroy frail enemy heroes. Dragon Slave, Light Strike Array, and Laguna Blade are incredible flaming nukes that can incinerate her target instantly, and Fiery Soul allows her to transition into a strong and fast physical attacker. Though her power falls from its peak late game, mana-boosting and damage-increasing items can be purchased to keep herself up, serving as the team's magical semi-carry, dishing out intense burning damage with her attacks and spells.

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 always 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.
 * However, Laguna Blade has a decent low cooldown, if you have a well supply of mana pool, you can use it to any enemy hero to burst out their health, and kill them if its necessary.
 * 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 base damage is already extremely high, so crit can be built early.
 * 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 survival-increasing / utility items will be of great use.
 * For Fiery Soul to take to its peak, cast Dragon Slave, Light Strike Array, and Laguna Blade successively to take the speed-enhancing effect of Fiery Soul to its maximum potential.

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.