What does "va'Yochach Amesh" mean?
Rashi: It means that the night before, Hashem had rebuked him (Lavan). 1
Ramban: It means that He proved him (Yaakov) right. 2
Why did Yaakov switch from "Elokei Avraham" to "Pachad Yitzchak"?
Ibn Ezra: "Pachad Yitzchak" means 'Yitzchak's fear of Hashem.'
Pane'ach Raza, Tosfos ha'Shalem (2): Lavan saw in a dream Yitzchak praying with great fear, lest Lavan harm him, and therefore he sent Devorah (to tell Yaakov to return). Lavan said (31:29) "Elokei Avichem Emesh Amar Elai," and not Elokecha - Hashem accepted Yitzchak's prayer, and warned me not to harm you.
Malbim: If not for Lavan's fear of [Elokei Avraham, who appeared to him and warned him, and] Yitzchak, who was a great noble, he would have harmed Yaakov.
Ha'amek Davar: This refers to his inability to see injustice.
Lev Eliyahu (Bereishis p. 107): This refers to Yitzchak's fear to bless Yaakov, lest he engage in matters of this world and wax rich, and his Shleimus will be blunted. 5
See Ramban, who equates this explanation with Targum Onkelos.
Moshav Zekenim asks that later Yaakov did so (refer to 32:10:1:1), and Eliezer said "Elokei Adoni Avraham" (Bereishis 24:42), four times in all (Chizkuni)! Riva answers for Eliezer that after the Akeidah, Hashem swore not to test Avraham again. (Refer to 32:8:4:4 to answer for Yaakov - PF.)
Rashi (to 28:13, citing Tanchuma): Since there is no guarantee that he will not sin before his death. Indeed, Hashem Himself said "Elokei Yitzchak" (28:13), because Yitzchak, whose eyes were dim and who was confined to the house, was unlikely to sin. (However, Yaakov was afraid to do likewise. - PF)
Perhaps he explains, "Had I not zealously retained my Shleimus, Hashem would not have done miracles for me, and you would have sent me away empty."
Why did Yaakov refer to his father's relationship with Hashem as "The fright (Pachad) of Yitzchak"?
Maharal #1 (Nesivos Olam, Nesiv ha'Teshuvah Ch. 2, p. 152): Yir'ah was indeed the trait of Yitzchak.
Maharal #2 (Derech Chayim 1:5, p. 37): Yitzchak's trait was Din (justice), and one involved in justice constantly fears lest he act in away that contravenes Yir'ah.
Having accused Lavan of cheating him right, left and center, why did Yaakov see fit to add that if not for Elokei Avi..., he would have sent him away empty-handed?
Rashbam: What he meant was that he would not have made him a farewell party, as he claimed he would have done. 1
See above, 31:27.
What are the implications of, "es Onyi ve'Es Yegi'a Kapai..."?
Oznayim la'Torah: Yaakov was telling Lavan that Hashem had seen how a. he suffered at the hand of Lavan; and b. how he toiled with integrity 1 - and had rebuked reuked him the previous night.
Why did Yaakov repeat, "Elokei Avi, Elokei Avraham"? Below, he said, "Elokei Avi Avraham" (32:10)!
Tosfos ha'Shalem (3): Elokei Avi refers to Yitzchak. 1
Ohr ha'Chayim #1: The G-d of my father Avraham is not like other gods, that do not save those who serve them. Rather, he is Elokei Avraham - Avraham publicized that the Creator has all ability, oversees, judges fairly and saves the oppressed.
Ohr ha'Chayim #2: Elokei Avi refers to the merit of his fathers. 2 He mentions their Midos; Elokei Avraham alludes to Chesed ("Chesed l'Avraham" - Michah 7:20), 3 and Pachad Yitzchak alludes to Midas ha'Din.
QUESTIONS ON RASHI
Rashi writes that Yaakov feared to attach Hashem's name to that of Yitzchak. Hashem Himself did so (28:13)! And Yaakov himself said "Elokei Avi, Elokei Avraha1m..."!