Travelers

Much like the Shan, Travelers invade a host's brain and take control of them. Unlike the Shan, however, Travelers are physical beings, and enter their victim's body through their mouth. They start off in a larval form (shown below) and mature once inside the host. Unlike the Shan, however, Travelers can't easily vacate their host.

In the RPG...

After a Traveler has matured inside its host—in only 3 days—it has the ability to shoot a nerve tendril out of its host's mouth, which will most likely paralyse its target. An average person has a 90% chance of being paralysed for 50 minutes. Presumably the other 10% would simply halve the time (with a Crit resisting it completely?). The Traveler then feeds on the blood of said target and uses the flesh to feed its host. They can also manipulate their host's body after death. These traits distinguish them significantly from the Shan.

In a video game...

Travelers in a video game would serve to create an atmosphere of paranoia, in that the player would not know who was infected until it was likely too late. The fact that they can live on even after the death of their host could also make for some interesting situations, essentially becoming instant zombies. Their tendril attack might be a little too dangerous, however. It has an 80% attack chance and being paralysed by the Traveler would pretty much mean instant death... or possession.

In a film...

Travelers have recently seen their on-screen debut in Cabinet of Curiosities. "The Autopsy" was adapted masterfully in what is easily the best episode of the series.