Tetsuya Nomura was a guest at the Magic Monaco Anime Game Conference where a new Kingdom Hearts 3 screenshot was shared, and the image was uploaded to twitter thanks to The Share Players!
The image shows off what looks to be a boss battle or large scale battle in Olympus Coliseum. Sora is in what looks to be Guard Form which was first revealed in October 2016.
UPDATE: Thanks to Dandelion, we have a translated portion of the Kingdom Hearts 3 part of Tetsuya Nomura's talk at Magic Monaco:
This is the first time we're showing this screenshot of Kingdom Hearts III, it's happening in Thebes and they are fighting a new type of Heartless. The Keyblade can transform into a lot of things. When in Power Form it can be changed into a chariot.
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