Among Survivor's deadliest creatures are the twin ninjas, which I sometimes call "Twin Traitors."
Now, your Twins are sort of a gestalt creature. Working as a team, each joins the fringe of a larger group. Each purports to be spying on the other group - - though what they mostly do is share info back and forth, claiming that they got it in spy missions or whatever..
Like the fistful of dollars ninja, the twin ninjas have the primary objective of driving two larger groups into conflict with one another. But it is harder to discover, because neither is ever expressly recognized as a spy. They give each other just enough info to cause the two groups to go to war - - usually with the most powerful personalities at the front - - and one ninja, behind each group, subtly pushing from behind. Its rather like a rope pulling contest, in reverse.
Expert twin killers can even recruit additional victims into the ranks of the vice-like killing machine they've constructed. And the amazing thing is that the anger level between the combatants runs so high, that no one ever realizes they've been viced.