Cards from the Classic Collection will not be legal in the Standard format
The flat edge of a D-ring keeps pages sitting flush against the spine instead of curving over a round surface meaningfully safer, but not bulletproof
Hexproof that protects a player, like Leyline of Sanctity, is a different challenge
Encore is one such ability from Commander Legends
However, solo play offers many opportunities for enjoyable games across various type-themed challenge decks
Keep in mind that the Pokmon TCG has grown into one of the largest card games ever printed: with over 15,000 individual cards in circulation, the question of how many pokemon cards are there has no single answer, but knowing which ones matter for Mewtwo specifically is exactly what this section is for