Hi for example, Kaheera, the orphanguard is my chosen companion. First game, pay 3 to get it from the sideboard then cast onto the field, it get killed and put into gy. On the second game is Kaheera shuffled into my deck, or is it back on the sideboard?
It is whatever you want; you are sideboarding after all. So, you can put it into your deck if you want. If you do that, it is no longer a Companion (or, more specifically, can't be declared as one). If you want to use it as your companion, you need to leave it in the sideboard and still ensure your main deck matches the condition after you are done sideboarding.
Hi for example, Kaheera, the orphanguard is my chosen companion. First game, pay 3 to get it from the sideboard then cast onto the field, it get killed and put into gy. On the second game is Kaheera shuffled into my deck, or is it back on the sideboard?
It is not part of your deck,
400.11. An object is outside the game if it isn't in any of the game's zones. Outside the game is not a zone.
400.11a. Cards in a player's sideboard are outside the game. See rule 100.4.
400.11b. Some effects bring cards into a game from outside of it. Those cards remain in the game until it ends.
Once the game ends, Kaheera is not part of the game anymore. The actions your performed during that game, such as bringing cards from outside the game to it, don't carry over to the second game.
While not playing a game, what you have is a list of cards that form your deck, and another list of cards that form your sideboard (including Kaheera). But as you are between games in a match, you can use the sideboard to modify the deck, so you may put Kaheera in your deck if you want to.
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It is not part of your deck,
400.11. An object is outside the game if it isn't in any of the game's zones. Outside the game is not a zone.
400.11a. Cards in a player's sideboard are outside the game. See rule 100.4.
400.11b. Some effects bring cards into a game from outside of it. Those cards remain in the game until it ends.
Once the game ends, Kaheera is not part of the game anymore. The actions your performed during that game, such as bringing cards from outside the game to it, don't carry over to the second game.
While not playing a game, what you have is a list of cards that form your deck, and another list of cards that form your sideboard (including Kaheera). But as you are between games in a match, you can use the sideboard to modify the deck, so you may put Kaheera in your deck if you want to.
thanks to both answers.
Nexus MTG News // Nexus - Magic Art Gallery // MTG Dual Land Color Ratios Analyzer // MTG Card Drawing Odds Calculator
Want to play a UW control deck in modern, but don't have jace or snaps?
Please come visit us at the Emeria Titan control thread