Why are the Makos listed in a different order than they occurred?
Radak: There was no need to write them in order; the order is known from the Torah.
Malbim (44): Here it teaches that the Makos were to show Hashem's strength. Therefore, each Makeh except for blood came double 1 . Arov and Tzefarde'a are taught together, for since all damaging 2 animals came with Arov, automatically Tzefarde'a came with them. Why did he send Tzefarde'a earlier by itself? Therefore it says that Arov ate them, and Tzefarde'a ruined them 3 .
Why does it say "Tzefarde'a" (singular)?
Refer to Shemos 8:2:1:1.
Radak: This is the Klal, like va'Ta'al ha'Tzefarde'a" (Shemos 8:2).
What do we learn from "va'Tashchisam"?
Mishnas Eliezer (19, p. 345): This includes all Chayos loose in the sea. Hashchasah is death - "va'Yomer David El Avishai Al Tashchisehu" (Shmuel I, 26:9).
Rashi: They removed their testicles.