The majority of them were chosen based on their strength in the standard competitive format, but a couple made the cut based solely on appearance
Base/Jungle/Gym earlier sets had 3 or 4 different variants
If a player has a card that says instant on it, they can play that card at any point in the game, even if its not their turn
Lutri, the Spellchaser Lutri, the Spellchasers only reason to be banned is if it were used as a companion, otherwise, it's a great, and fair elemental otter that doesn't need to live on the Game Changer list
Aside from this, its also great fun just to play the game
Lastly, as this often indestructible God causes you to draw a card whenever it attacks, you can reliably use it to draw an additional card on each of your turns without needing to worry about it dying in combat