What is the significance of a slave that rules?
Rashi (31): Nebuchadnetzar was a slave of Merodach Bal'adan and wrote his letters (refer to 30:25:2:1).
Malbim (Derech ha'Muskal): Imagination rules over Batei ha'Nefesh, in place of Sechel. Imagination was created to be a slave to Sechel, and to obey its commands. When it overpowers Batei ha'Nefesh and speech, the land is agitated. It pillages Emes, concocts lies and matters with no existence, and casts doubt on everything faithful and lasting. Or, it entices hearts to believe every folly. This is the level of the Evvil or Pesi that were explained in this Sefer.
Malbim (Derech ha'Pashut): Alkum rebelled and became king.
What is problematic if a Naval is satiated with food?
Rashi (31): This is Achashverosh, who made a feast for 180 days.
Malbim (Derech ha'Muskal): A Naval did not gather the laws of Chachmah into his noble Nefesh. He gathered only obscenity and folly, and he thinks that he is satiated with bread of Chachmah. This is Chacham b'Einav that was explained several times. He thinks that all his deeds are with Chachmah.
Malbim (Derech ha'Pashut): If a Nadiv is satiated, he influences from his good to the poor. A Naval does not; he increases his evil.