Command: !fave <card ID>
Tag a card as a favorite. You can tag multiple cards as your favorite. You can only set cards that you own as favorite. If you give a favorited card to another user using !givecard, the card will automatically be removed from your favorite cards list. When people use !view to view a card that you have set as favorite, it will be noted in the footer of the embed that the card is set as your favorite, to inform them that a card is not up for trades.
Related:
!favelist: See list of favorites
!givecard: Give a card to other user
!view: View a card’s details