Sideboard

Sideboard is a separate set of up to fifteen cards a player can swap into their deck between games of a match, in place of cards already in the main deck. It exists so players can adapt to a specific opponent rather than playing one fixed list all match long.

After game one, both players usually know roughly what the other is playing, and the sideboard is how they respond to that information before game two.

How Sideboarding Works

Between games, a player can swap any number of cards between their main deck and sideboard, as long as the main deck returns to its legal minimum size. A common change is bringing in extra removal against an aggressive deck, or added disruption against combo.

Cards swapped out for one game can be swapped back in for the next, so sideboarding is a per-game decision made fresh each time a match continues.

Building a Sideboard

A well-built sideboard covers the deck’s known weaknesses, with targeted answers for aggressive decks, control decks, and any combo strategies that are popular in the current metagame.

On MTG Arena, sideboarding only comes up in Best-of-Three queues and events. Best-of-One matches use a single game with no sideboard, which pushes deckbuilders toward decks that are already well-rounded from the start.