Source: Dr. Who
Location: Edge of the galaxy, but they do get about.
Threat Assessment: 7. An entire race of highly technological beings with a militant culture. They are from a high gravity environment and are very strong and tough.
Limitations: In a war already with the Rutins. They have one big weakness. The probic vent at the back of their necks is highly susceptible to damage. A good whack there can take a Sontaran down. One reason Sontarans never back down from a fight.
Sontarans are all clones so there isn't a lot of genetic variety there.
Personal note: Love how they look like a cross between trolls and Volgons. I also like that they really don't care much about humans. They only get in our face as they work out how to beat the Rutins.