Cynthia returns, but as a Sun & Moon alternate artwork promo in Expanded format.
You can obtain this Cynthia 155/S-P promo as a participation award at these Extra Battle Day tournaments that will be held starting from January 23, 2021 at Pokémon Card Gym stores in Japan. This Cynthia is a Sun & Moon (alternate artwork) card reprint, and will be an Expanded card.
Update 31-12-2020: Added image with promo number and higher resolution.
You need to purchase 6 packs to enter and only Expanded decks are allowed.
A special playmat containing artwork used that was originally used for the Kanto Friends Mini Tin released in 2019 and illustrated by Naoki Saito, is also given away if you win the tournament or win a rock-paper-scissors challenge.
No other images have been revealed yet. The previous Extra Battle Day promo's were Hau 394/SM-P, Acerola 395/SM-P, Guzma 396/SM-P and Lillie 397/SM-P released in 2019. Lillie 397/SM-P is currently worth over $3000 USD now in Japan.