Tournament rule 403.4
Players may use sideboard cards to modify their deck in between games of a match. In constructed, sideboard cards must be exchanged 1 for 1 with Main Deck cards.
- 403.4.a During that time, a player may change their Chosen Champion to one from their sideboard or Main Deck that meets the…
- 403.4.b In constructed formats, a player may not change their Runes, Legend, or Battlefields at any point after deck…
- 403.4.c After the sideboarding process, a player’s Main Deck must meet deck size requirements dictated by the competition…