You usually earn promo cards by completing solo battle challenges, and they have different art and attacks than standard cards
Grave Pact [Best Creature Sacrifice Enchantment] Blacks entire sacrificing things for power gig is already pretty cool, but it can be even better with Grave Pact , which essentially forces your opponent to play the same game as you
0-cost cards One thing that wont be included in the list are 0-cost cards, like Black Lotus, Lotus Petal, or Ornithopter
Or a specific concept/theme
Lands, creatures, phases, spells: its all there
If a player always takes the top half of the deck with their right hand, and then shuffles so that the cards in their right hand are slightly higher than their left, the top card will never change