What did Hashem mix in Egypt?
Rashi: He mixed a drink for them; he made their Ru'ach crooked. "Masach" is like "Maschah Yeinah" (Mishlei 9:2). Mixing a drink in a barrel, until it has the proper taste, is called Masach.
Radak: He confused their counsel and destroyed their Chachmah. Masach is mixing, like "b'Yayin Masachti" (Mishlei 9:5).
Malbim: He put in them a spirit of confusion and insanity, like one who mixes wine so it will be pleasant to drink. Egypt drank from this intoxicating wine, and became drunk.
What is "Iv'im"?
Rashi: It is the name of an illness of insanity.
Radak: It is from the root Avah - Na'avah Lev (a crooked heart).
Who made Egypt stray?
Refer to 19:13:3:1-2.
"Ma'asehu" implies that Egypt is masculine. Verse 13 ("Pinas Shevateha") implies that it is feminine!
Radak: Sometimes the verse uses the feminine for the assembly, and sometimes it uses the masculine for the nation.
What is the comparison to a drunkard staggering in his vomit?
Radak citing Targum Yonasan: He errs in his thoughts and tramples in his liability. I.e. he does not know what to do, and vomits, and afterwards rolls in his vomit.
Malbim: A drunkard strays to return to drink his vomit, which his innards and stomach expelled, for it cannot bear it. He thinks that it is wine, and he drinks it. So [the officers] misled Egypt to do deeds against their nature, for which the land will vomit them out, and it cannot contain them 1 .
Sifra (Kedoshim 4, 12:14): Eretz Yisrael is unlike all other lands. It does not tolerate transgressors, and vomits them out! Malbim's words require investigation. (PF)