Each block has had five Planeswalkers since Scars of Mirrodin. We already know four and so the last should be in Journey into Nyx. As you know from my post about Ajani he will probably be the fifth. In this post I will remind you of the first four Planeswalkers and show you a new spoiler True-or-False for the Journey into Nyx Ajani.
Born of the Gods
Journey into Nyx