What is "Shot"?
Rashi: It is a plague of afflictions.
Radak: It is harsher than Shevet and Mateh. [Sancheriv] hit you with a Shevet, and Hashem will hit him with Shot.
What is the comparison to "Makas Midyan"?
Rashi: They were killed in one night, and the kings that fled from them were killed - "Orev b'Tzur Orev 1 " (Shoftim 7:25). Also [Sancheriv], after he will return to his land, will die there via the sword.
Malbim: Hashem aroused Machaneh Midyan to strike each other due to fear of Hashem that came on them; He will do so to Machaneh Ashur 2 .
Radak: Also "v'Es Ze'ev Hargu v'Yekev Ze'ev" (ibid). Here it mentions only Orev, like one who mentions the initial matters. The matter is known in Sefer Shoftim.
What is the meaning of "u'Matehu Al ha'Yam"?
Rashi: [Hashem] will arouse against Sancheriv also His staff that was on the sea, against Pharaoh and his army. Malbim - this will be totally via Hashem. His angel will kill and burn them.
Radak: [Melech Ashur's] staff that he raised against you, will be like Pharaoh's staff at the sea. There, Hashem's anger against him was completed, and Hashem raised His staff on him. The prefix Kaf in "k'Makas" applies also to this.
Why does it say "u'Nesa'o [b'Derech Egypt]"?
Rashi: He will remove him from the world, like He did to Egypt. Radak - He drwoned them in the sea. So He will wipe out Machaneh Ashur in Yerushalayim.
Malbim: This is a metaphor, as if Melech Ashur will go in the way of Egypt when he returns from Tirhakah Melech Kush against Yerushalayim, like Rashi brings below (37:36) from Seder Olam. He passed by Yam Suf, and took from there Hashem's staff. He brought it to Eretz Yisrael, and there Hashem sturck him with it.
