Who are "Anshei Rachil"?
Radak: They go tale-bearing from the weak to the strong 1 , in order to spill innocent blood. Malbim - this is one of the three ways in which they murdered. The others are via the Nesi'im (6), and via bribery (12). These correspond to three Midos that remove a person from the world. Rechilus corresponds to envy, bribery corresponds to Ta'avah, and the Nesi'im correspond to honor.
I.e. the weak tell the strong what others did, so the strong will kill them. (PF)
What is the meaning of "v'El he'Harim Achlu Vach"?
Rashi citing Targum Yonasan: In the mountains they served idolatry in you (Yerushalayim).
Radak (18:6): They used to offer sacrifices on mountains, like it says 1 , and eat them there. "El" is like Al; the same applies to many verses.
I.e. "Avdu Sham ha'Goyim? Eloheihem Al he'Harim" (Devarim 12:2). (PF)
What Zimah did they do?
Rashi, from Targum Yonasan: It is counsel of sin.
Radak: This is a Klal for all Arayos; later, some are detailed.