I can certainly get you started. You can take this answer and add your own examples and insights to it.
In the poem you mention, the frog serves as the archetypal vilain. He is rude to his fellow bog-mats; he is manipulative, jealous and greedy. He hates the joy that the nightingale brings to the bog and is jealous of the talent her singing receives. Worst of all, he feels no remorse for anyone he hurts.
Villains hate beauty, and the frog is no different. He decides to capitalize on the situation by pretending to befriend the nightingale, who has never been subjected to this kind of manipulation. He forces her to conform to his will. He charges admission for the chance to hear her sing, forces her to practice in adverse conditions and continually scolds the poor bird, pushing her until she dies.
Notice the animals have no names. The nightingale can represent anyone with a true talent and love for something. The frog is the person who uses this talent for his own means. Think of a parent whose child is gifted in a sport. How many times can that parent scold and push that child to hate a sport he once loved?
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