Mewtwo EX & Reshiram have been revealed from the S8a 25th Anniversary Collection set.
Reshiram has been revealed and will be part of the main set of the S8a 25th Anniversary Collection set. You can play this card in standard format.
Also Mewtwo EX originally released here in Black & White - Next Destinies, will be part of the 25th Anniversary Edition Promo Card Pack. It will get a reprint with foil and from what it seems, texturing treatment.
This card is almost a direct reprint of it's original version, and as such, may not be used in official Tournament play.