Remans are notable for being sensitive to light. At least some Remans have telepathic abilities.
The Remans were an insignificant faction in Alpha Quadrant politics until the 2370s, when they acquired the technology to develop a thalaron weapon that allowed them to overthrow the government of the Romulan Empire. With that coup, they became a threat comparable to the other Alpha Quadrant powers. Since their defeat in Star Trek: Nemesis (including the death of their leader, Shinzon), they may have become an insignificant threat again.