Historically, the most useful sideboard cards are silver bullets. These cards are narrow in scope but incredibly powerful, and they occupy sideboard slots dedicated to beat the hardest opponents. Silver bullet sideboard cards are found everywhere formats with large card pools like Legacy and Modern.  These formats feature older sets with powerful color-hosers and hate cards not often printed today. These formats also breed powerful combo decks, which forces other decks to play specific answers. Modern sideboards are defined by these narrow but powerful answers, and they are going to play a huge role in the outcome of Grand Prix: Richmond.

Torpor Orb

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Modern is filled with enter-the-battlefield abilities. The most notable is Snapcaster Mage, but  Torpor Orb is played specifically as a hate card for combo decks. The Splinter Twin combo relies on the abilities of Pestermite and Deceiver Exarch, while the Melira Pod  combo relies on the abilities of persist creatures. Torpor Orb stops both combos, making this artifact one of the most effective and universal sideboard options in the format.

Choke

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 Choke  is one of the most oppressive sideboard cards in the format, along with its vicious red cousin Boil. The banned list changes were great for blue, and as blue gets better, so does blue hate. Choke has applications against everyone playing Island and blue shocklands, including Splinter Twin combo, Storm combo, and UWR Control.  If a blue deck makes the mistake of tapping out, Choke starts to look as good as, if not better than, Blood Moon.

Stony Silence

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 Stony Silence is the premier artifact hoser in the format. It does incredible work against Affinity, which is still the fastest aggressive deck in the format. Stony Silence also punishes the Urza Tron deck, which relies on artifacts to fix its mana. While these two archetypes were not hugely popular at the Pro Tour, they are going to be a significant presence in the Grand Prix metagame.

Rest in Peace

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Rest in Peace is to the graveyard as Stony Silence is to artifacts. It removes both graveyards when it hits play and prevents cards from ever entering the graveyard. It turns off everything related to the graveyard, including Tarmogoyf, Snapcaster Mage, Scavenging Ooze, Past in Flames, persist creatures, Voice of Resurgence,  Knight of the Reliquary, Living End, and Life from the Loam. Stony Silence is one of the most underplayed cards in the entire format and one of the best options for the sideboard of white decks.

Rule of Law

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Storm combo is probably the most inherently broken deck in Modern,  While Splinter Twin doesn't always aim to play a fair game, it at least has a fair game plan.  Storm does not; either it combos, or it loses.  It is minimally interactive, one-dimensional, singularly focused, and fast. It is also the deck most vulnerable to dedicated hate. The best hate card against Storm combo in Modern is Rule of Law. This eliminates both of their main paths to victory, Grapeshot and Empty the Warrens. Rule of Law will require a dedicated answer like Echoing Truth to be beat, which puts the burden on the combo player. A creature-oriented option is Ethersworn Canonist, which is faster but vulnerable to a commonly played Storm sideboard card, Lightning Bolt.