Except via rules, special actions, and effects that specifically bring cards into Commander games from outside the game, traditional cards from outside the game cannot be brought into a Commander game.
July 23, 2021 · Adventures in the Forgotten Realms
If a player is allowed to bring a card from outside the game into a Commander game, that player can’t bring a card into the game this way if it has the same name as a card that player had in their starting deck, if it has the same name as a card that the player owns in the current game, or if any color in its color identity isn’t in the color identity of the player’s commander.
April 17, 2020 · Ikoria
If a player is allowed to bring a card from outside the game into a Commander game, that player can’t bring a card into the game this way if it has the same name as a card that player had in their starting deck, if it has the same name as a card that the player has already brought into the game, or if any color in its color identity isn’t in the color identity of the player’s commander.
July 13, 2018 · Core Set 2019
Brawl Option
July 22, 2016 · Eldritch Moon
rule 903.11 not present in this release
January 16, 2016 · Oath of the Gatewatch
The Commander variant includes the following specification for winning and losing the game. All other rules for ending the game also apply. (See rule 104.)
July 17, 2015 · Magic Origins
If a commander would be exiled from anywhere or put into its owner’s hand, graveyard, or library from anywhere, its owner may put it into the command zone instead. This replacement effect may apply more than once to the same event. This is an exception to rule 614.5.
February 1, 2014 · Born of the Gods
If a commander would be put into its owner’s graveyard from anywhere, that player may put it into the command zone instead.
September 30, 2011 · Innistrad
If a commander would be put into its owner's graveyard from anywhere, that player may put it into the command zone instead.
June 17, 2011 · Commander 2011
If a commander would be put into its owner’s graveyard from anywhere, that player may put it
April 1, 2011 · Duel Decks: Knights vs. Dragons
If a commander would be put into its owner's graveyard from anywhere, that player may put it into the command zone instead.
February 4, 2011 · Mirrodin Besieged
If a commander would be put into its owner’s graveyard from anywhere, that player may put it into the command zone instead.
October 1, 2010 · Scars of Mirrodin
If a general would be put into the exile zone from anywhere, its owner may put it into the
February 1, 2010 · Worldwake
If a general would be put into the exile zone from anywhere, its owner may put it into the command zone instead.