As you rank up more and more cards will be accessible through pvp packs. Each rank floor also has specific locker rewards and pvp packs. If you want the best rewards you’ll have to rank up to legendary. Once you reach legendary you’ll get the same reward regardless of your legendary rank.
Note that the newest released card is only available through special event lockers. This card is listed as available in rank 1 but this is specifially ment to be only for the event packs.
How many alien visitors did you count?