Which two things did Hashem see, that caused Him to "change His mind" and made Him sad (Kevayachol)?
Seforno: He saw that he had been evil up until now and that all his thoughts were focused on sinning further, so that there was no chance that he would pay any attention to anyone who came to rebuke him.
What is "Kol Yetzer...Rak Ra Kol ha'Yom"?
Peninim mi'Shulchan ha'Gra: One who is defeated in war, he becomes weak. When one defeats his Yetzer ha'Ra, it becomes stronger - "the greater the person, the greater his Yetzer" (Sukah 52a).