1)
What is "Mechukak"?
1.
Rashi: It is what is written in Torah. All the more so [there is concern lest he forget] Girsa (oral Torah).
2.
Malbim: It is Chukim and creed.
2)
Why does it say "vi'Shaneh Din Kol Bnei Oni"?
1.
Malbim: Via drinking, he will forget, and change the law of all Bnei Oni. All of them come in front of him for judgment. The laws must be guarded in his heart to judge correctly.
