To date, this is the last Pokemon movie to take place in the main series' continuity.
The next generation Pokémon in this movie is #801, Magearna. It is the Generation 7 Mythical Pokémon as well.
A Mega Sableye appears on the main poster for this movie as a member of Alva's army. However, it is not present in the movie itself.
After the flower field is destroyed by the flying fortress's laser, the sound of Magearna screaming is removed from the dub.
Of all Pokemon movies to star Mythical Pokémon, this is the first time more than one has a starring role.