My best guess was that seven is one of the more common numbers for card games where you draw cards and perhaps it won out because it was what Richard Garfield thought people would assume to draw
But its extra powerful here because it also exiles a card from one opponents library each turn and lets you play it
5 Felothar, Dawn of the Abzan Felothar, Dawn of the Abzan strides onto the battlefield with the commanding presence youd expect from an Abzan war-leader.Their ability to sacrifice a nonland permanent whenever it enters, or attacks, turns even your smallest tokens, clues, and enchantments into fuel for teamwide +1/+1 counters
You can also group your cards by rarity, card type, or price
[129] [130] Promotional crossovers [edit] Wizards of the Coast has introduced special cards and sets that include cross-promotional elements with other brands typically as promotional cards, not legal for Standard play and may not be playable even in eternal formats