What is "v'Mashal Pi"?
Rashi: It is Divrei Torah.
Radak citing Ibn Ezra: They are "Noshekei Romei Kashes", "La'aroch Shulchan ba'Midbar", "v'Esh Niskah v'Yakov", "v'Dalsei Shamayim Pasach" and "Degan Shamayim" (verses 9, 19, 21, 23- 24).
Malbim: All early nations, their vain Emunah had many stories about the source of their gods. The priests of the idols fabricated them; they were a parable for Chachmah or Musar dressed in a story. There were two shortcomings. (a) The story was false. (b) The parable was in riddles and hidden matters. Commoners did not understand it; only Chachamim understood. Commoners accepted the fabricated stories simply - they inherited Sheker and folly, as is known from their songs to the idols and mythology. Stories of the Torah are different; refer to 76:3:1:2.
What are the riddles?
Radak citing Ibn Ezra: "Lechem Abirim Achal Ish" (verse 25, refers to Haman), "va'Yiten la'Shevi Uzo" (verse 61, refers to the Aron). These are elusive; we would not know [the latter] if not that Sefer Shmuel discusses the exile of the Aron. Radak - also "Bnei Efrayim Noshekei Romei Kashes" (verse 9) is a riddle. It is not clear which war this discusses.