But what sets Modern Horizons 3 apart are the cards you've never seen before
In 2010, an MTG Duel Deck pack was printed with a Reserved List card included

1 Mirko, Obsessive Theorist 1 Marvo, Deep Operative 1 Case of the Shifting Visage 1 Copy Catchers 1 Final-Word Phantom 1 Watcher of Hours 1 Charnel Serenade 1 Eye of Duskmantle 1 Foreboding Steamboat 1 Unshakable Tail 1 Counterpoint 1 Ransom Note (Surveil) 1 Amphin Mutineer 1 Dream Eater 1 Mission Briefing 1 Phyrexian Metamorph 1 Sphinx of the Second Sun 1 Vizier of Many Faces 1 Black Sun's Zenith 1 Dogged Detective 1 Doom Whisperer 1 Grave Titan 1 Massacre Wurm 1 Overseer of the Damned 1 Phyrexian Arena 1 Pile On 1 Reanimate 1 Rise of the Dark Realms 1 Toxic Deluge 1 Twilight Prophet 1 Baleful Strix 1 Connive // Concoct 1 Lazav, the Multifarious 1 Master of Death 1 Choked Estuary 1 Darkwater Catacombs 1 Drownyard Temple 1 Fetid Pools 1 Hostile Desert 1 River of Tears 1 Sunken Hollow 1 Brainstorm 1 Consider 1 Curate 1 Deep Analysis 1 Enhanced Surveillance 1 Ephara's Dispersal 1 Mulldrifter 1 Nightveil Sprite 1 Otherworldly Gaze 1 Thoughtbound Phantasm 1 Animate Dead 1 Necromancy 1 Price of Fame 1 Ravenous Chupacabra 1 Shriekmaw 1 Sinister Starfish 1 Syr Konrad, the Grim 1 Whispering Snitch 1 Dimir Spybug 1 Discovery // Dispersal 1 Disinformation Campaign 1 Notion Rain 1 Arcane Signet 1 Dimir Signet 1 Everflowing Chalice 1 Mind Stone 1 Sol Ring 1 Talisman of Dominance 1 Thought Vessel 1 Ash Barrens 1 Bojuka Bog 1 Command Tower 1 Dimir Aqueduct 1 Myriad Landscape 1 Mystic Sanctuary 1 Port of Karfell 1 Reliquary Tower 1 Rogue's Passage 1 Tainted Isle 1 Temple of the False God 1 Tocasia's Dig Site 9 Island 9 Swamp Revenant Recon Tokens 4 Copy // Zombie tokens 4 Salamander Warrior // Zombie tokens 1 City's Blessing (helper) // Zombie token 1 Vizier of Many Faces // Zombie token Copy // Zombie Salamander Warrior // Zombie City's Blessing (Helper) // Zombie Vizier of Many Faces // Zombie Deadly Disguise Kaust, Eyes of the Glade and Duskana, the Rage Mother are traditional foil cards

I'm NOT providing card-for-card swaps for these, but the general rule of thumb is take out cards that fulfill the same role but worse: take out a land for a land, removal for removal, card draw for card draw, etc
Artifact - Equipment Swiftfoot Boots Equipped creature has hexproof and haste
Enough cEDH players who we trust have convinced us that it is the only change they need for the environment they seek to cultivate