Starfinder: Strigs
One of the stranger undead creatures found, this monster was created through the use of necromancy and genetic tinkering. The actual creature is a tiny, 1 inch long albino worm that needs blood to survive and it does need a host to live in. The worm uses its host like a literal vehicle and colony all at once.
The creature can only use humanoid creatures as hosts, and cannot use any non-humanoids. They will not even attempt to infect any non-humanoid. An infected creature will undergo a drastic change (see above) and once it is complete they will have a swollen throat, a jaw which can be unhinged, and are completely hairless and porcelain white. Black veins can be seen beneath the skin (even though the blood is now white) and the flesh appears to be moving as if filled with tiny worms (which in fact, it is).
Once fully transformed, the Strig has a fully prehensile tongue. The throat appears to be swollen, and the jaws can become unhinged to allow the tongue to shoot out from the host with a fifteen foot reach.
Also, the worms take over the mind of the host; effectively killing it (only a Miracle or Wish can reverse this). Once this happens, the host will only seek out to feed and protect itself from sunlight (or any manner of UV radiation). The worms can access the memory of the host and use it to bring them to more fertile feeding grounds, and the worms take a perverse pleasure in going after the hosts original family (if any).
Once the host reaches this state, it will only use its hands to try and bring down a victim (beating on them), or it will use its new prehensile tongue like a ranged weapon to attempt to feed off (and in the process, infect) a new victim. After the tongue has successfully struck, the victim must overcome the Strig’s CMD (26) to remove it.
It is said that once the host has been controlled by the worms for 30 days, the last changes have taken place and the worms develop into a hive mind, which replaces the hosts mind entirely (but they retain the host’s memories).