Dota 2/Riki the Stealth Assassin

""I've been here the whole time.""

Riki is a melee agility carry hero who is known for being very elusive. He can stay invisiable forever with his Permanent Invisibility, stalking his enemies without them even knowing. His Smoke Screen helps him evade attacks as well as disabling enemies, while his Blink Strike is excellent for chasing or escaping. All of these skills help set up his deadly Backstab, which amplifies his damage as long as he is behind his enemy.

Smoke Screen
Smoke Screen makes a lingering puff of smoke appear in the target area, silencing, slowing as well as causing enemy attacks in the smoke screen to miss. A helpful disable to let you escape enemies or catch up to them. Remember that since enemies can only be affected by the Smoke Screen if they stand in it, you should put them in the direction of where they will be instead of where they are, for a better chance of catching them longer.
 * Ability: Target Point
 * Radius: 250 / 275 / 300 / 325
 * Miss Rate: 40% / 50% / 60% / 70%
 * Slow: 25%
 * Mana Cost: 75 / 80 / 85 / 90
 * Cooldown: 13

Blink Strike
Blink Strike makes you blink behind the target unit, striking it for bonus damage if it's an enemy. It increases your mobility, but only if there are units that you can blink to. You can use it to catch up to an enemy, placing you conveniently in the position to activate your backstab, or to escape by blinking to a nearby ally.
 * Ability: Target Unit
 * Damage Type: Magical
 * Damage: 30 / 60 / 90 / 120
 * Range: 700
 * Mana Cost: 50
 * Cooldown: 20 / 15 / 10 / 5

Backstab
Backstab will let you do a bonus amount of damage depending on your agility stat provided that you attack your opponent from behind. With your invisibility and Blink Strike, it should be quite easy to get behind an opponent for a backstab. If your target is fleeing, it actually makes them more suscaptible to backstabs since their backs will be facing you.
 * Ability: Passive
 * Damage Type: Physical
 * Agi Damage Mult: 0.5 / 0.75 / 1 / 1.25

Permanent Invisibility
Permanent Invisibility, as the name suggests, lets you stay invisible permanently, only dropping it temporarily when attacking or using an ability. This is why Riki is so deadly. You can easily appear from nowhere and take an enemy by surprise. Be careful that you don't get silenced, since you will lose your invisibility for the entire duration of the silence.
 * Ability: Passive
 * Fade Delay: 3 / 2.25 / 1.5

Suggested Skill Build
Skilling Riki is rather simple, but slight adjustments must be made to fit your general situation. One thing that's consistent in all skill builds is to get your ultimate, Permanent Invisibility, as soon as you can, at level 6, 11 and 16. It is your signature ability, and you'll have much more difficulty ganking or surviving without it.

Standard skill build
Get Smoke Screen at level 1, since it is a very useful disable that lasts a relatively long time, helping you escape early ganks. Then get Blink Strike for a spammable escape mechanism and chasing tool. From level 3 you can choose whether to max Blink Strike or Backstab first. Prioritize Blink Strike if you find yourself getting ganked or going for ganks a lot, so that it becomes more spammable and gives you some extra damage. If your opponents are playing more passively or you have a great lane support that lets you farm comfortably, get Backstab to get easier last-hits. Max Smoke Screen last as its duration and slow remains constant through all levels.

Starting items
Get any combination of Iron Branches, Healing Salves and Tangos. Also get some Slippers of Agility to increase your damage for easier last-hitting.

Early-game items
You can choose to get a Magic Stick and upgrade it into a Magic Wand for some burst healing in case of enemy ganks. Get Boots of Speed for more speed and your eventual boot upgrade. You can choose to get a Poor Man's Shield if you're taking a lot of harassment. You might want to upgrade your Slippers of Agility into some Wraith Bands for some more damage and good stat bonuses.

Mid-game/Core items
For your boot upgrade, get Power Treads for extra damage, survivability and flexibility. Diffusal Blade is a great item for Riki, as it gives you a nice damage boost. The Purge ability it grants you is especially useful, as it grants you an additional disable, while it can also remove any debuffs that reveals your invisibility.

Luxury/Situational items
A Vladmir's Offering is a commonly bought item for Riki, but there are better choices. It's cheap and gives you lifesteal and damage, but it isn't worth an inventory slot during the late-game. A Butterfly is an excellent item for any agility carry, as it will give you a huge boost to your dps. You can also consider getting a Sange and Yasha for a mix of survivability and damage. An Assault Cuirass will also boost your damage with the attack speed bonus and armor reduction, but it can reveal your location to smart enemies. Lastly, a Black King Bar makes you immune to any disables, including invisibility-revealing silences, letting you take down your foes without fear of dying.