What is the significance of "Koreh Shachas Bah Yipol"?
Rashi: Bil'am gave counsel to Balak, and caused 24,000 Yisraelim to die. He came to Midyan to claim his wage, and Yisrael killed him.
Malbim: He himself will fall in the pit that he dug.
Why does it say "v'Golel Even Elav Tashuv"?
Rashi: He rolls a rock to a place where people will stumble on it, in the end he will stumble on it.
Rashi citing Agadas Bereishis 2: This refers to Avimelech - he killed his 70 brothers on one rock, and in the end he died via a rock - "va'Tashlech Ishah Achas Pelach Rechev Al Rosh Avimelech va'Taretz Es Gulgaso" (Shoftim 9:53).
Malbim: He rolls a rock to a place where it will harm his colleague - it will return to [harm] him.