Its not just about scarcity its about the cultural crossover between Pokmon and art
Whenever Umbris or another Nightmare or Horror enters the battlefield under your control, target opponent exiles cards from the top of their library until they exile a land card.
While this isnt a formal rule, the concept behind summoning sickness is
Azami, Lady of Scrolls Azami, Lady of Scrolls | Illustration by Ittoku Commander (1) Planeswalker (2) Jace, Wielder of Mysteries Narset, Parter of Veils Creature (21) Archaeomancer Baral, Chief of Compliance Cyclone Summoner Glen Elendra Archmage Jace, Vryn's Prodigy Laboratory Maniac Lighthouse Chronologist Malevolent Hermit Patron Wizard Sea Gate Stormcaller Snapcaster Mage Sower of Temptation Spellseeker Thassa's Oracle Tribute Mage Trinket Mage Triskaidekaphile Trophy Mage Vedalken Aethermage Vendilion Clique Venser, Shaper Savant Instant (24) Aetherize Arcane Denial Archmage's Charm Blue Sun's Zenith Brainstorm Counterspell Cyclonic Rift Dig Through Time Dispel Dramatic Reversal Frantic Search High Tide Long-Term Plans Mana Drain Mental Misstep Muddle the Mixture Mystical Tutor Negate Pact of Negation Pongify Rapid Hybridization Reality Shift Swan Song Turnabout Sorcery (4) Expropriate Fabricate Step Through Windfall Enchantment (4) Back to Basics Mind Over Matter Mystic Remora Rhystic Study Artifact (11) Arcane Signet Extraplanar Lens Isochron Scepter Mind Stone Mana Vault Sapphire Medallion Sensei's Divining Top Sky Diamond Sol Ring Thought Vessel Throne of Eldraine Land (33) Snow-Covered Island x27 Mystic Sanctuary Nykthos, Shrine to Nyx Path of Ancestry Reliquary Tower Riptide Laboratory Seat of the Synod Prior to my ventures into the world of Urza, Lord High Artificer, I was deep in the trenches of Azami, Lady of Scrolls wizards
