
Commander creatures you ownCommander creatures you ownAny creature that is your commander, wherever it is. This is how a Background gives its ability to the commander it is paired with. have "At the beginning of your upkeep, exile the top card of your library. This creature gets +X/+0 until end of turn, where X is that card's mana valuemana valueThe total amount of mana in a card's cost, ignoring colour. A card costing has mana value 4. X counts as 0 except on the stack.. You may play that card this turn."
Hover an underlined rule to see what it means.
Read from the rules text. A card that enables a keyword makes or is the thing; a card that rewards it gets better when you have it. Two cards interact when one enables what the other rewards.
A Background can be a second commander alongside any creature with Choose a Background.