Templar Assassin

Lanaya the Templar Assassin is a short-ranged Agility hero capable of dealing huge bursts of Physical damage to swathes of enemies with expert positioning and timing. Unlike most physical damage dealers, Lanaya reaches her damage potential quite early and then scales up from that point with carry items, letting her gank with impunity throughout the mid-game, and her range changes from a melee hero to a ranged hero with short reach as she levels Psi Blades.

Her Psionic Traps provide map control and the ability to chase down fleeing heroes from up to 2000 range, and Refraction and Meld lets you shrug off high-damage nukes and disjoint projectiles. With a Blink Dagger, Lanaya can quickly materialize in the enemy team's weakest flank and shred several heroes at once with her Meld and Psi Blades.

Tips

 * Refraction is highly desirable to level up first, as the increased number of instances is key in playing mindgames. The attack damage increase is also significant.
 * Although leveling Meld will give Lanaya even more damage, it can be difficult to get in attack range to use it effectively without points in Psi Blade. If your team has disables that will give you time to move up into range, or if you have the advantage and can rush a Blink Dagger, Meld is a good choice. Otherwise, Psi Blade will grant you a bit more presence and safety during fights.
 * Use Psi Blades as a harass. It has a great spill radius, and not only can it be used to farm more effectively, but also to harass heroes. (If you are soloing the mid lane or otherwise.)
 * Place Psionic Traps at the rune spawn points to gain vision.
 * A ward will still be better for more vision of the surroundings, and to free up traps for your own usage.

Trivia

 * In DotA, Templar Assassin makes numerous references to the game Starcraft, another famous RTS game by Blizzard. Her ability to manipulate psionic energy, the psi blades she wields, and the mention of her master being originally from Aiur in her DotA biography all apply to the Protoss, one of the three main races of the game.