In the Star Wars timeline, the last time we saw Yoda was at the end of Return of the Jedi as the heroes were celebrating what was thought to be the end of the Empire. Yoda was absent in Star Wars: The Force Awakens, but he might appear again in this year's Star Wars: The Last Jedi.
The hint of Yoda appearing in Star Wars: The Last Jedi was implied by an interview Frank Oz (voice of Yoda) had with Variety. The website specifically asked him if Yoda is set to appear in the new movie. You can read Oz's response to that question below.
I feel like I'm a prisoner at war here, and I can only give you my name, rank and serial number. To be true to the people who asked me, and they are kind of my family, I have to say I've been asked not to talk about it. I love Yoda. I would be happy to talk to you about it at the time they let me.
This is a sign that Yoda might be in the new movie if Frank Oz is refusing to talk about it. Disney/Lucasfilm usually bans actors from telling secrets about their movies. Daisy Ridley has had to dodge many bullets recently as people have been trying to ask her who Rey's parents are.
It's highly possible Yoda might make an appearance to give guidance to Luke Skywalker as a Force Ghost. This time the roles are reversed somewhat as Luke is now the mentor teaching about the Force to Rey. Yoda could just have a small cameo as it's unlikely he'll have a huge part in the movie.
Anyway, Star Wars: The Last Jedi is releasing on December 15th, 2017 in North America. It is the eighth episode in the main series of Star Wars films.
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