Dota 2/Viper the Netherdrake

Viper is a ranged agility hero that is usually played as a carry. Despite his average health he can be quite durable with his Corrosive Skin. Viper can do more damage the lower an enemy's health with his Nethertoxin. He can use his Poison Attack to slow enemies down as well as poisoning them. His ultimate, Viper Strike, is one of the best slows in the game, slowing enemies to a crawl.

Poison Attack
Poison Attack is a toggled ability that makes your normal attacks slow enemies as well as do damage over time. It is a Unique Attack Modifier and will not stack with other Unique Attack Modifiers. While it can be auto-cast to apply the effects to your attacks as long as you have mana, it is not reccommended since you will make creeps attack you and possibly run out of mana quickly. A good ability to harass opponents or to simply chase down dying enemies.
 * Ability: Auto-Cast, Target Unit
 * Affects: Enemy Heroes
 * Damage Type: Magical
 * Duration: 2
 * Damage Over Time: 10 / 16 / 22 / 28
 * Move Slow: 10% / 20% / 30% / 40%
 * Attack Slow: 10% / 20% / 30% / 40%
 * Mana Cost: 20
 * Cooldown: 4 / 3 / 0 / 0

Nethertoxin
Nethertoxin lets you do bonus damage based on how much health an enemy is missing. For every 20% health missing, the bonus damage will double. The bonus damage is halved against non-hero units. At level 4 you can do a maximum of 160 damage every attack, which is pretty significant. Very helpful for chipping down and finishing off enemies.
 * Ability: Passive
 * Damage: Physical
 * Base Bonus Damage: 2 / 4 / 6 / 8
 * Non-Hero Damage: 50%
 * Max Bonus Damage: 40 / 80 / 120 / 160

Corrosive Skin
Corrosive Skin grants you bonus magic resistance that fully stacks with your base magic resistance and items. It also slows any enemy that attacks you as well as dealing damage over time. This ability can make it hard to take Viper down in a duel. Enemies trying to attack you will not only find it harder to chase you and take you down with their high dps, but will also be losing more health as they attack. The bonus magic resistance also helps when there are powerful spellcasters on the enemy team.
 * Ability: Passive
 * Damage Type: Magical
 * Durarion: 4
 * Move Slow: 10% / 15% / 20% / 25%
 * Attack Slow: 10% / 15% / 20% / 25%
 * Magic Resistance: 10% / 15% / 20% / 25%
 * Damage Over Time: 10 / 15 / 20 / 25

Viper Strike
Viper Strike will slow a targeted enemy as well as poison them, doing damage over time. At level 4 it's a crippling 80% slow, meaning your enemies will have very little chance of escaping you. It can either be used to initiate a kill or to finish an enemy off.
 * Ability: Target Unit
 * Affects: Enemy Heroes
 * Damage Type: Magical
 * Duration: 5.1
 * Damage Over Time: 60 / 100 / 145
 * Move Slow: 40% / 60% / 80%
 * Attack Slow: 40% / 60% / 80%
 * Mana Cost: 125 / 175 / 250
 * Cooldown: 80 / 50 / 30
 * Scepter Cast Range: 900
 * Scepter Mana Cost: 125
 * Scepter Cooldown: 12

Aghanim's Scepter can be bought by Viper and will increase Viper Strike's cast range as well as reduce its mana cost and cooldown.