Not only does this provide you with easier access to the rarity symbol, youre also only going to be checking for just that symbol, rather than reading the card name or ability box

Honda, Sumo Champion Creatures (23) 1 Alms Collector 1 Burnished Hart 1 Daxos, Blessed by the Sun 1 Elesh Norn, Grand Cenobite 1 Esper Sentinel 1 Evangel of Heliod 1 God-Eternal Oketra 1 Indomitable Ancients 1 Kitsune Loreweaver 1 Kor Cartographer 1 Knight of the White Orchid 1 Mangara, the Diplomat 1 Mentor of the Meek 1 Nyx-Fleece Ram 1 Prava of the Steel Legion 1 Reverent Hoplite 1 Solemn Simulacrum 1 Springjack Shepherd 1 Wall of Omens 1 Weathered Wayfarer 1 Welcoming Vampire 1 Wild-Field Scarecrow 1 Zetalpa, Primal Dawn Planeswalkers (2) 1 Elspeth, Sun's Champion 1 Karn, Scion of Urza Instants (8) 1 Flawless Maneuver 1 Generous Gift 1 Path to Exile 1 Release to Memory 1 Rootborn Defenses 1 Sejiri Shelter // Sejiri Glacier 1 Swords to Plowshares 1 Teferi's Protection Sorceries (3) 1 Emeria's Call // Emeria, Shattered Skyclave 1 Martial Coup 1 Mass Calcify Enchantments (7) 1 Crackdown 1 Brave the Sands 1 Felidar Retreat 1 Land Tax 1 Search the Premises 1 Smothering Tithe 1 Thorough Investigation Artifacts (19) 1 Archaeomancer's Map 1 Ebony Fly 1 Ensouled Scimitar 1 Fountain of Ichor 1 Gilded Lotus 1 Guardian Idol 1 Hedron Archive 1 Lightning Greaves 1 Mind's Eye 1 Nyx Lotus 1 Robe of Stars 1 Slagwurm Armor 1 Skullclamp 1 Sol Ring 1 Staff of Nin 1 Swiftfoot Boots 1 Thought Vessel 1 Venser's Journal 1 Whispersilk Cloak And there we go

1 paper playmat
What purpose did it serve
Realmwalker - Casting cards from the top of your library is always great for card advantage
In the incredibly rare case where, during your cleanup step, Ancient Adamantoise is phased out with damage marked on it, Ancient Adamantoise's second ability won't apply and all marked damage will be removed from it during that cleanup step