Lord Shiva to take the form of Hanuman

Lord Vishnu begins to narrate the tale of Ram bhakt, Hanuman, and starts by how the Gods of the five elements and the sapthrishis in distress, had visited the abode of Lord Vishnu, with a cry for help. As Vishnu finds out that Raavan has made inappropriate use of the boon bestowed by Brahma on him, he decides to bring an end to this demon, himself. He declares that he will be taking the human form of Lord Ram. At the same time, Lord Shiva is seen chanting the name of Lord Ram. Parvati sees him curiously and enquires about this new name that she has heard for the first time. Shiva goes on to explain about Vishnu's divine plan and adds that he too will be a part of this war of good versus evil, as he will be taking the form of Ram bhakt Hanuman. How will Lord Vishnu and Shiva bring an end to the egoistic Raavan?