How that came about was that the artist, Ron Spencer, was turning in a sketch for the art director to sign off on, and instead of handing in a sketch of some scary creature, he turned in a picture of a little mouse with hot cocoa to make the art director laugh
An Eevee Heroes booster box contains 30 booster packs, and each pack comes with 5 random cards
(The game has reportedly made millions since launch.) In gaming, this is known as gachaa gameplay mechanic not unlike putting a quarter in a vending machine and hoping for the trinket you want
Out of the 69, 21 are promo cards which may be a bit trickier to find, but with 38 common rarity cards, you wont have much trouble getting your hands on some
This could be easily accomplished with Grinder Golem or the Scrap package