1)
What does "Od Zos" refer to?
1.
Rashi: They increased to do [evil] when I brought them to the land. Malbim - they sinned three times before entering, and a fourth time after entering - "v'Al Arba'ah Lo Ashivenu" (Amos 1:6).
2)
Why does it mention "Gidefu Osi"?
1.
Malbim: Giduf is reviling Hashem's name in public - "veha'Nefesh Asher Ta'aseh b'Yad Ramah... Es Hashem Hu Megadef" (Bamidbar 15:30). Mena'etz is b'Mezid and denial.