The Nephilim were the children of the fallen angels and natural women. Genesis 6:4 (NASB), “The Nephilim (giants) were on the earth in those days, and also afterward, when the sons of God (fallen angels) came in to the daughters of men, and they bore children to them. Those were the mighty men who were of old, men of renown.” This scripture reports that the hybrid race, Nephilim, continued to be born and lived until the flood. However, all of these souls were drowned in the flood.
1 Peter 3:20 teaches that only Noah, his wife, his three sons and their three wives survived the flood: “…the longsuffering of God waited in the days of Noah, while the ark was a preparing, wherein few, that is, eight souls were saved by water.”
Noah, himself, “was a just man and perfect in his generations, and Noah walked with God.” Genesis 6:9. The phrase, “perfect in his generations,” means that Noah had not interbred with the fallen angels. Consequently, none after the flood carried Nephilim heritage. All born subsequent to the flood were of pure Adamic or human stock.
Since Nimrod was born after the flood, Genesis 10:8,9, he did not have super human powers. He was fully a man.