Sideboarding

1. What can be in your sideboard? [Source: WotC]
   Sideboards can contain 1 character card of 20 stars or fewer and up to 10 battle cards.
   • No more than 3 copies of each Battle Card are allowed between a player's deck and sideboard.
   • Duplicate character cards are not allowed between players' decks and sideboards.
   • After sideboarding, decks must be legal.
2. How do you sideboard? [Source: WotC]
   After each game in a match, the player who won that game chooses to sideboard a character
   first, and declares their team. Then, the player who lost the previous game does the same. Then
   both players swap battle cards between their main deck and sideboard simultaneously.
   Players are not required to reveal how many battle cards they have swapped from their main
   deck to their sideboard and do not have to swap one for one, but after sideboarding, their
   sideboard may not exceed the maximum sideboard size (10 battle cards).
3. Can I put stratagems in my sideboard? [Source: WotC]
   Yes. Each one counts as one of your ten battle cards in the sideboard.
4. Can I put a card with head mode or body mode in my sideboard? [Source: WotC]
   You can but note that each card is a separate character card. This means you could have a character card with a head mode or one with a body mode in your sideboard, but not both.
5. If I open a card in a Limited Format that says "grab a card from outside the game" am I allowed to dip into my personal collection for this (assuming I brought it ahead of time) or just the sideboard of my Limited Pool? If I have a lesser collection (or am just lazy), am I allowed to use cards from my Sideboard for my Outside-of-the-Game-Board? Or is this a Head Judge for an event decision? [Source: WotC]
   For casual play, you are allowed to use whatever parameters your play group has decided on. For competitive play, in Limited, you are only allowed to draw "outside the game" cards from your Limited pool. Editor's Note: In our initial ruling, we misstated our answer and accidentally ruled that "outside the game" cards must be limited to one's sideboard. This is incorrect.

   They later changed competitive rules to require battle cards to come from the sideboard.
6. Is it legal to have a copy of Swap Parts in my Side Board that I never put into my actual deck? [Source: WotC]
   No, it is not legal. It is so not legal in fact, that it is illegal.
7. During sideboarding, if I want to swap a character for a stratagem, when does that happen? [Source: Aequitas]
   When you change your characters. You present your starting team (including stratagems) before swapping battle cards.