In a new trailer for Pokemon Sun & Moon released by CoroCoro, an unidentified and possibly new Pokemon is seen in video game footage from overworld gameplay. The Pokemon is seen on the left at the 12-second mark of the new trailer.
Above is a screen grab showing the unidentified and possibly new Pokemon.
The trailer is mostly the same as the one released on May 10 by Nintendo that showcased the three new starters: Rowlet, Popplio, and Litten. However, there is some new footage that shows the player trainer exiting their home and walking around.