Viper

The viper is a new strain of zerg fliers being incorporated in the upcoming expansion StarCraft II: Heart of the Swarm.

Vipers contain a thick microbial "soup" in their abdomens, which they fire at ranged enemies, damaging their weapons systems. The viper can siphon bioelectrical energy and nutrients from other zerg buildings.

Game Unit
Vipers are classified as "battlefield manipulation units." They are hive-level caster units with no other pre-requisite building.

Vipers are meant to give the zerg an extra edge in clearing out chokepoints, allowing the short-range zerg units to stand a better chance against long-ranged ones.

In matches against protoss, vipers are particularly effective against colossi due to their abilties (see below).

Upgrades
In the campaign, the Viper is an evolution of the Mutalisk with some changes. Abduct costs much less energy, and Blinding could prevents shooting from beneath the cloud entirely.

Development
The concept of the viper goes as far back as 2008. It resembled a snake/scorpion in this form. Concepts were done by Samwise Didier. Its current aesthetic is a cross between a cobra/scorpion and a wasp.

As of April 2012, the viper could also "eat" minerals in order to recover energy. This renders the patch unavailable, so it should not be used in the player's base.

Cut Abilities

 * Ocular Parasite: The viper grants detection to an allied non-massive unit. The viper can target other vipers or itself with this ability. It can only be used once. This ability has probably been removed as of April 2012, since the overseer has been returned, and the viper made into a "pure" spellcaster.

Special Viper Strains

 * Cobra (cut content)

Trivia
The viper is David Kim's favorite new zerg unit in Heart of the Swarm.