>>77378506They included a meme Sakana card that is banned from competitive play, so they can add cards if they want when they want. They could have started with Gen1/Gen2/Invaders but likely didn't because of initial balancing issues for the base game.
They could add Rinmama if everything lined up legally, but nobody knows for sure. Like picrel was a meme fan-made card. The artist who drew it said in the replies that they consent to it, but the interpretation of Rinmama is based off of a fan design by Roober. So is there an extra layer of consent needed because this is a licensed game?