Genestealer

The Genestealers are among the most insidious bio-forms of the Tyranids, a clawed, six-limbed vanguard organism dispatched ahead of the great hive fleets to prepare worlds for consumption. Swift, cunning, and horrifyingly strong, a lone Genestealer can slaughter squads of armed defenders in the dark, its scything talons shearing through armour and flesh alike. But its most terrible weapon is not its claws: it is its infectious embrace.

When a Genestealer implants its genetic material into a host, the victim is subtly corrupted, and their offspring are born tainted with Genestealer DNA. Over generations this spreads through a population, giving rise to a hidden Genestealer Cult: a secret society of mutated worshippers bound in psychic thrall to their patriarch, who venerate a coming saviour they do not understand to be their own doom. These cults burrow into the fabric of a world, awaiting the day the fleets arrive.

When the Hive Mind's hunger finally descends, the cult rises in open revolt, throwing a world into chaos precisely when it must be strongest. The very defenders meant to repel the swarm are revealed as its heralds, and the planet falls from within before the first bio-ship darkens the sky. In this way the Genestealers embody the Tyranid threat at its most patient and terrifying: a corruption that turns a world's own children into the vanguard of its devouring.