Tyranids
The Tyranids are an extragalactic composite species of hideous, insectoid xenos. They actually comprise an entire space-faring ecosystem comprised of innumerable different bioforms which are all variations on the same genetic theme.
The Tyranids are unlike any other intelligent species encountered by Humanity. They are the ultimate predators; to them, all living things, from the lowliest insect to the most advanced starfaring civilisation, are mere prey. Only now are the inhabitants of the galaxy realising the scale of the threat; unless the Tyranids can be stopped, it will mean nothing less than the extinction of all life.
Brood Brothers kt24
Brood Brothers are the humans of the Genestealer Cults, who have been implanted by Genestealers and have served as hosts for their Genestealer Hybrid offspring.
Infiltration Vanguard kt24
Hosts of vanguard organisms including lictors, leapers and other stealthy tyranid creatures are typically sent before a full scale attack to damage enemy supply lines and key targets. While these creatures typically work alone, sometimes it's necessary to organize and take out an important foe.