Hive-Fleet Sisyphus

Description
A recently discovered Hive-Fleet that has appeared on numerous lifeless planetoids, the immense swarm known as 'Hive-Fleet Sisyphus' has been spotted throughout the galaxy. Various studies have tried to understand their curious behaviour of avoiding life-filled worlds that other Hive-Fleet had done all in their power to devour, or becoming frenzied upon the discovery of a Forge World. 

The most current theorem is the suggestion that their nature is similar to scavengers as they follow other Hive-Fleet, consuming any form of rock, stone, or metal that had to be left behind or was otherwise indigestible.

Tyranids of Note

• Merope - An uncomfortably mobile Norn-Queen that has been spotted near the frontlines by the Imperium within several costly encounters with Hive-Fleet Sisyphus. The Tyranid Lifeform known as 'Merope' is a hulking machine of flesh that can violently devour a Mechanicus Kastelan within seconds and birth swarms of Warriors within the same disturbing moment.
• The Gûllynbûrsti - A known menace to several Kindreds of Votann, this Tyranid lifeform was born to counter a test vehicle of the Deep Rock Kindred specifically designed to travel within the bio-organic structures of the Hive-Fleet's largest vessels. During the conflict, this modified Hekaton Land Fortress was successfully disabled as the Tyranid lifeform destroyed the glass, devoured the crew, and inadvertently became trapped within it's hull. Thus the Gûllynbûrsti was named as it used it's newly found armour to successfully damage a Hearth, before disappearing thanks to an attempted plasma bombardment.