Common pitfalls players make when building their sideboard is adding cards that are good vs fringe decks, matchups that are already fine, or trying to overcompensate for that one matchup your deck is bad against. There’s no need to go overboard; Modern is a wide format, so pick cards that cross-perform against several decks, not only a select few (unless, of course, you know what the field is). 

These 15 cards should also complement the main, not be a separate entity. UW Control is great at being flexible and switching roles, such as having a transformational beatdown plan from the sideboard, but know which role you’ll be playing in the given matchups.

If you’re a seasoned Modern player, you’ve likely noticed the way metagames cycle through competitive decks, which are often pillars of the format. You can’t count out well-designed, inherently good decks for too long. For instance, Do0mSwitch’s sideboard philosophy when Hogaak and Phoenix were the decks to beat, was to start with 3 Rest in Peace, then pick 12 other cards. That’s not to say it’s wrong to play less, but this is part of the deckbuilding groundwork he’s built for himself. Shortcuts like this are key to winning in Modern

By acknowledging this principle, focus on establishing a consistent formula and core, then tweak your flex spots to adapt to meta trends or hedge against weaker matchups. Design your sideboard to cohesively complement the maindeck, but choose cards that cross-perform against common archetypes/gameplans instead of targeting specific cards/matchups, such as:

• Aggro/Midrange/Control/Combo
• Graveyards
• Artifacts
• Small Creatures/Burn
• Spells
• Lands