Tyranids: Venomthropes

Venomthropes are specialized Tyranid support bioforms that act as living chemical weapon dispensers. They drift across the battlefield, emitting dense, yellowish clouds of toxic spores that both shield allied Tyranids and poison any non-Tyranid life forms. 
Physical Characteristics
Form: They have scrawny, floating bodies supported by gas bladders and numerous whip-like tentacles.
Tentacles: Their "Toxic Lashes" are coated in highly potent poisons; a single touch is often lethal enough to dissolve organic tissue.
Size: They are typically supplied on 40mm round bases and stand as moderately tall infantry units. 
Role on the Battlefield
Defensive Cover: Their primary function is generating a Spore Cloud. In current gameplay (10th Edition), this provides the Benefit of Cover to all friendly Tyranids within 6" and gives the Stealth keyword (-1 to be hit) to non-monster units.
Terraforming: On a larger scale, the Hive Mind uses them to poison a planet's atmosphere and soil, preparing the biosphere for total consumption.
Offense: While primarily defensive, they are effective against enemy infantry due to their Anti-Infantry 2+ melee profile, meaning they wound most infantry on a roll of 2 or higher. 
Miniature Kit
The Venomthrope is sold as an 80-piece plastic kit that can alternatively be built as Zoanthropes or a Neurothrope.