PHemius and Medon
He compared them to "Fish that fishermen drag from the churning gray surf". You can find this information in Book XXII at line 409
Odysseus begins plotting his revenge once he learns of the suitors, but he does not start killing them until Book XXII, after threading his bow, and shooting it through the twelve axes' handles.
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In the Odyssey book, they are people who are basically fortune tellers or prophets.
He is the herald (town messenger) of Ithaca. When Odysseus comes back to Ithaca, his hometown, Telemakhos (Odysseus' son) tells Odysseus not to kill him. Unlike the suitors, he cared for Telemakhos while his father was away and remained loyal to Odysseus. Therefore, he was not killed in Book XXII.
Homer
No
In book 11 of the Odyssey The Gorgon is mentioned, not the name of Medusa.
Odysseus returns to Ithaca in Book 13 of The Odyssey. This is where he meets with his loyal swineherd, Eumaeus, and begins to plan out his revenge against the suitors.
Poseidon is in Ethiopia in Book 1 of the Odyssey.
Book II
The only thing Hermes took with was a bag with food. Odyssey is a book.