What are "Rosh Perazav"?
Rashi: The heads of his open cities and villages 1 . This is like "Perazos Teshev Yerushalayim" (Zecharyah 2:8), "me'Arei ha'Perazi" (Devarim 3:5).
Radak: His soldiers' heads. His soldiers are called Perazav because multitudes will come, and they will dwell around Yerushalayim like people of open cities who spread everywhere - there is no wall to enclose them. Gog will say "E'eleh Al Eretz Perazos [... b'Ein Chomah]" (Yechezkel 38:11), "Perazos Teshev Yerushalayim me'Rov Adam" (Zecharyah 2:8).
Why does it say "Nakavta v'Matav Rosh Perazav"?
Rashi: Sancheriv was a staff with which You ruled over nations. When he came to scatter me, You punctured his troop leaders with the staff that he came to rule over me via them.
Radak: With Gog's own staffs You will puncture his soldiers' heads. Hashem will send frenzy among them - one will puncture and crush his friend's head - "Tihyeh Mehumas Hashem Rabah Bahem" (Zecharyah 14:13), "Cherev Ish b'Achiv Tihyeh" (Yechezkel 38:21).
Malbim: This begins the third part of the Tefilah. It discusses when great afflictions beset Yisrael; Mezid water floods over their heads. This was during the Galus, for two reasons. (a) When nations gathered to destroy Yisrael, and killed them with all harsh deaths, and the Yishmaelim, when their Navi rose, they all gathered to swallow and destroy Yisrael with Shemados (decrees against Mitzvos) and Avadon. (b) When they did not make a general Shmad, they consumed them with the entire mouth in hidden ways, and took their property and money. Nakavta teaches that when you spoke and decreed, when the nations tilted the staffs of their wings and soldiers, when Roshei Perazav (his troops) that gathered from the open cities. Multitudes headed to Yerushalayim to conquer Eretz Yisrael. The same applies when troops of Yishmaelim spread to fight the war of their Emunah. Then you spoke your decree. These troops will storm on Yisrael to scatter them and expel them from their land and eradicate them. Whenever multitudes gathered to fight for their Emunah, they killed many of Yisrael.
Why does it say "Yis'aru Lahafitzeni"?
Rashi: Sancheriv and his entourage were stormy winds to scatter me.
Radak: They will come in a storm wind against me to scatter [Yisrael] amidst the nations.
What does the verse teach about their Simchah?
Rashi: It is when they are able "Le'echol Ani ba'Mistar."
Radak: Their Simchah is to scatter me, like they thought to do at the sea. Yisrael left Egypt, and they thought to consume them with Simchah - "Amar Oyev Erdof Asig" (Shemos 15:9).
Malbim: When they did not openly destroy them, their Simchah was if they can covertly consume a Yisrael. They consumed poor Yisraelim covertly, and harmed individuals and stole their money.
Does this truly refer to Aniyim?
Rashi: It refers to Yisrael, who are called "Ami Oni" (Tzefanyah 3:12).
Radak: Yes, the Aniyim of Yisrael.
What is the significance of "Le'echol Ani ba'Mistar"?
Radak: Pharaoh thought that Hashem does not see, and His power is not at the sea like it was in Egypt.