In last week’s tournament rules tip it was pointed out that at sanctioned events you are required to present your sideboard before a match. One other rule regarding your sideboard is that you should not keep any cards that are not a part of your deck or sideboard with your sideboard. According to the Magic infraction guide, any cards that are kept with a sideboard are considered to be a part of it. If upon being deck checked you have cards with your sideboard that should not be there you can receive a penalty for Deck / Decklist Error. At competitive and professional REL events, the proscribed penalty for this is a game loss.

Judge staff may downgrade this penalty if the cards kept with this sideboard could not ‘conceivably’ be played. For example if the card is not legal in the format. However it is still a good idea to keep all other cards completely separate from your sideboard.