I used illustrator for this and let me tell you this was a rather big challenge. But I am quite happy with the results so please tell me what you think and if you like it, vote!!
So here I choose Medusa, the Hydra, and the Erinyes. In the corners of the picture is the owl, olive leaves, and snakes: all of which represent Athena, Goddess of War/Wisdom.
I know the Hydra is not as well connected to Athena as the others, but it is said that she may have been the muse (in a sense) for it's defeat.
Medusa was defeated by Perseus, who had met with Athena on the way. She assisted him as well as the God Hermes.
The Erinyes tormented a man named Orestes who had killed his mother under orders of Apollo. He ran to Athena for help, who arranged a trial and bribed/threatened the Erinyes.
I'm not an expert on Greek Mythology but I did do research to create this. So I hope you enjoy.