From 1d4chan

Ursarax are similar to the Thallax in design and are the Mechanicum's Assault Marines equivalents. Ursarax are advanced Jump Pack-equipped Tech Thralls of the Adeptus Mechanicus designed in the later Great Crusade. They were first designed by Magos Explorator Enabrin Falkan as a heavy, rapid-moving close combat unit. Using a fusion of existing technologies sacred to the Mechanicum, materials and patterns taken from the Thallax of the Ordo Reductor, and the fruits of Falkan's own discovery, he created a unit of mass rape.

Like the Thallax, they are Thralls rather than Servitors, selected from suitable human candidates for conversion so their living components retain a consciousness and dim recollection of their former selves. Neural anesthesia is automatically administered for the successful fulfillment of their orders, providing them with temporary relief from their tortured existence. After Falkan's mysterious disappearance, his warring acolytes dispersed to many different masters, taking the secret of the Ursarax with them. It is unknown if any Ursarax are still in existence, but chances are that they are probably mothballed in a museum for the Tech Priest to goggle at, knowing the Mechanicum nowadays.

Ursarax are equipped with Lightning Claws and Volkite Incinerators. Great for tearing apart MEQ's and GEQ's alike. Far more useful than Chaos Warp Talons that for sure. They also have a hug of doom (get it? Ursa, like bears) for TEQs.

Forces of the Adeptus Mechanicus
Command: Magos (Tech Priest Dominus - Tech-Priest Manipulus)
Troops: Chrono-Gladiator - Combat Servitors - CATs - Electro Priest - Enginseer
Kataphron Battle Servitors - Myrmidon - Pteraxii - Secutarii - Serberys Raiders
Serberys Sulphurhounds - Servo-Automata - Skitarii - Tech Priest - Tech Thrall
Thallax - Ursarax
Castellan-class robot - Cataphract-class robot - Colossus-class robot
Conqueror-class robot - Crusader-class robot - Scyllax-class robot
Thanatar-class robot - Vultarax stratos-automata - Ambot
Walkers: Ironstrider Ballistarius - Onager Dunecrawler - Sydonian Dragoon
Vehicles: Chimera - Karacnos Assault Tank - Krios Battle Tank - Land Raider
Macrocarid Explorator - Minotaur Artillery Tank - Rhino Transport
Skorpius Hover Tank - Triaros Armoured Conveyer
Flyers: Archaeopter - Avenger Strike Fighter - Lightning Fighter - Storm Eagle
Other: Galvanic Servohauler - Ordinatus
Titans: Dire Wolf Heavy Scout Titan - Imperator Battle Titan - Imperial Knight
Reaver Battle Titan - Warbringer Nemesis Titan - Warmaster Heavy Battle Titan
Warhound Scout Titan - Warlord Battle Titan
Spacecraft: Fury Interceptor - Starhawk Bomber - Shark Assault Boat