This is because it gives your commander creatures the ability, it's not an effect of the Background itself
This depends on the popularity of the card within competitive play, the age of the card, number of cards printed, and various other factors
I could not pick a favorite (as to me they're all beautiful), but if I was to choose one to highlight, it would be Mountain #106
Christesen's plans of opening first in hopes of establishing large and disruptive plays came in direct conflict with how the deck is constructed
This green, blue, and red deck wants those massive creatures out quickly so theres a healthy mix of ramp, cost reduction for Dragons, and mana rocks to help keep you consistent
You may choose the same mode more than once