1)
What is "Mapetz"?
1.
Radak: It is a Kli used to shatter rocks - "v'Ish Kli Mapatzo b'Yado" (Yechezkel 9:2). Niputz is breakage with scattering of the pieces. When one breaks rocks, the pieces scatter all around.
2.
Metzudas Tziyon: It is a Kli used to demolish walls.
2)
Who is a Mapetz of Hashem?
1.
Rashi: Bavel. Until now, I used you to destroy and shatter the nations upon which I decreed exile.
2.
Malbim: Yisrael. Via (i.e. due to you), I will shatter Bavel, which was Hashem's weapon [to destroy other nations]. "Goyim" refers to the nations of Bavel and their kingdoms.