I had both Raff Capashen and Jhoira’s Familiar on the board which are supposed to reduce the cost of Historic cards. JII is a legendary spell and the cost was not reduced by either card.
Also when I cast it with Jhoira’ Weatherlight Captain on the board it did not cause her to trigger her ability. I believe that while it has the Legendary symbol it is not being counted as a Legendary card.
//Edited Title -Brigby