1)
What is the grammatical form of "Mosei"?
1.
Radak: Mosim is a noun, from Mes, just like Onim from On. When it is Samuch, it is Mosei. This is like "v'Es Ashir b'Mosav" (Yeshayah 53:9)
2)
What is the Chidush that they will die like Arelim?
1.
Radak citing Targum Yonasan: This refers to Resha'im, i.e. Arlei Lev.
2.
Malbim: They will not kill you like they kill a king or G-dly person, rather, like they kill Arelim, disgracefully.
