What are the connotations of "Venasati es Yadi be'Mitzrayim"?
Rashi: It means Hashem's Hand Mamash. 1
Oznayim la'Torah: When Par'oh will not listen to the Mofsim, Hashem will stretch out His Hand against the bodies of the Egyptians. 2
Presumably this refers either to Makas Dever
To which great judgments is Hashem referring?
Seforno: To Makas Bechoros and the drowning of the army in the Yam-Suf, which came as a punishment Midah K'neged Midah for their cruel treatment of Yisrael. 1
Seforno: The purpose of the other plagues was to bring Par'oh to do Teshuvah. Seforno: See Beshalach, Sh'mos 14:18, and to demonstrate Hashem's Omnipotence to Yisrael. See Sh'mos 7:17, Sh'mos 8:18, Sh'mos 9:29 and Sh'mos 10:1,2.