Missing sideboard cards? The full 15-card sideboard runs about $141.
Buy sideboard on ManapoolSolitude answers Devourer of Destiny or Glaring Fleshraker before they snowball, though exiling their threats gives them life rather than buying you time against Emrakul, the Promised End turns. Pithing Needle on Malevolent Rumble is not applicable since it's a sorcery with no activated ability, so instead name Basking Broodscale's adapt ability; Devourer of Destiny has static/triggered abilities that are not targetable either, and Eldrazi Temple's mana abilities are immune, but Needle successfully stops Boseiju, Who Endures' channel ability from hand as a reliable target. Stubborn Denial is weak since it only stops noncreature spells and most of their threats are creatures, but it can catch Kozilek's Command. We trim slow utility (Forge Anew, Meticulous Archive, Paradise Mantle, Lavaspur Boots) for more interaction since this matchup is a race against their ramp into giant threats.
This is a race where their Lightning Bolt, Lava Dart, and Unholy Heat can snipe our small threats, so Sanctifier en-Vec is excellent, granting protection from red while also removing their Dragon's Rage Channeler delirium fuel from graveyards and indirectly denying flashback synergy for Monastery Swiftspear prowess triggers. Solitude flash-blocks or answers a Slickshot Show-Off or Dragon's Rage Channeler to stabilize against the burn plan. We trim the cheap artifact filler (Ornithopter, Paradise Mantle) and slow pieces (Meticulous Archive, Lavaspur Boots, Forge Anew) that don't affect the race enough.
Teferi, Time Raveler is outstanding here, shutting off their Ephemerate and Flickerwisp flicker tricks and Solitude flash interaction during our turn while also bouncing a problematic Overlord of the Balemurk or Orcish Bowmasters and drawing a card. Pithing Needle can name Emperor of Bones or Kaito, Bane of Nightmares to blunt a recurring value engine. We shave a copy of slower utility pieces (Forge Anew, Meticulous Archive, Paradise Mantle, Lavaspur Boots) since this matchup is about resolving and protecting one big threat under Thoughtseize pressure rather than grinding with extra equipment.