Complex sentence: The chorus of frogs sings the famous croaking onomatopoeic refrain: (Greek:)--greatly annoys Dionysus, who engages in a mocking debate (agon) with the frogs.
Split into simpler sentences: The chorus of frogs sings the famous croaking onomatopoeic refrain: (Greek:). This greatly annoys Dionysus, who engages in a mocking debate (agon) with the frogs.