The seller, smpratte, is a well-known figure in the Pokmon community and noted in the description that this card is rarer than Honus Wagner, Mickey Mantle, Black Lotus, and even Charizard
(Scryfall note) Abilities that Slivers grant, as well as power/toughness boosts, are cumulative
Featuring the legendary brothers Monkey D
With that in mind, let's look at those "pokemon Animn Pokemon Cards", shall we
Mega SPOILER: Click to show For generation 1 there are 15 Mega Pokmon in total (Venusaur, Blastoise, Charizard X, Charizard Y, Beedrill, Pidgeot, Alakazam, Slowbro, Gengar, Kangaskhan, Pinsir, Gyarados, Aerodactyl, Mewtwo X, Mewtwo Y), of which 13 are available on TCG cards (Mega Pinsir is not available, and Mega Gyarados is only available as Shiny Mega variant)
It doesnt get much better