Companion

MTG Mechanic

You can have up to one chosen companion for each game. That chosen companion doesn't start in your main deck. Rather, it's a card in your sideboard. This means it doesn't count as a card toward meeting the minimum deck size in the format you're playing, but in Constructed formats, it is one of your fifteen sideboard cards. Just before the game begins, reveal your chosen companion to all players. Once during the game, but only during your main phase if the stack is empty, you can pay {3} to put your chosen companion into your hand.