To be given a Grade 10, a card would need to be deemed perfect with four sharp corners, and a front and back that are free of any impressions, indentations, or minor abrasions, PSAs website states
All those Magic players, drawing their cards, slinging their spells
Here's a list of each Dominaria United Jumpstart Booster and what you'll find in them: Coalition Corps 1 Serra Redeemer (Jumpstart Booster rare) 1 Random white rare or mythic rare, or Karn, Living Legacy 1 Clockwork Drawbridge 1 Resolute Reinforcements 1 Argivian Cavalier 1 Charismatic Vanguard 1 Captain's Call 1 Griffin Protector 1 Argivian Phalanx 1 Prayer of Binding 1 Join Forces 1 Love Song of Night and Day 5 Plains 1 Full-art stained-glass Plains 2 Traditional foil Plains 1 Theme description card Coalition Legion 1 Serra Redeemer (Jumpstart Booster rare) 1 Random white rare or mythic rare, or Karn, Living Legacy 1 Samite Herbalist 1 Benalish Faithbonder 1 Knight of Dawn's Light 1 Argivian Cavalier 1 Charismatic Vanguard 1 Griffin Protector 1 Take Up the Shield 1 Prayer of Binding 1 Join Forces 1 Love Song of Night and Day 5 Plains 1 Full-art stained-glass Plains 2 Traditional foil Plains 1 Theme description card Mystic Mischief 1 Cosmic Epiphany (Jumpstart Booster rare) 1 Random blue rare or mythic rare 1 Coral Colony 1 Soaring Drake 1 Academy Wall 1 Talas Lookout 1 Tolarian Terror 1 Frostfist Strider 1 Impulse 1 Impede Momentum 1 Ertai's Scorn 1 Founding the Third Path 5 Island 1 Full-art stained-glass Island 2 Traditional foil Island 1 Theme description card Arcane Mischief Cosmic Epiphany (Jumpstart Booster rare) Random blue rare or mythic rare Haunting Figment Soaring Drake Academy Wall Talas Lookout Frostfist Strider Djinn of the Fountain Impulse Shore Up Combat Research Impede Momentum 5 Island 1 Full-art stained-glass Island 2 Traditional foil Island 1 Theme description card Totally Ruthless 1 Tyrannical Pitlord (Jumpstart Booster rare) 1 Random black rare or mythic rare, or Weatherlight Compleated 1 Cult Conscript 1 Phyrexian Vivisector 1 Splatter Goblin 1 Phyrexian Rager 1 Gibbering Barricade 1 Sengir Connoisseur 1 Bone Splinters 1 Cut Down 1 Battle-Rage Blessing 1 Braids's Frightful Return 5 Swamp 1 Full-art stained-glass Swamp 2 Traditional foil Swamp 1 Theme description card Totally Merciless 1 Tyrannical Pitlord (Jumpstart Booster rare) 1 Random black rare or mythic rare, or Weatherlight Compleated 1 Knight of Dusk's Shadow 1 Phyrexian Vivisector 1 Eerie Soultender 1 Phyrexian Rager 1 Sengir Connoisseur 1 Writhing Necromass 1 Battle-Rage Blessing 1 Pilfer 1 Braids's Frightful Return 1 Extinguish the Light 5 Swamp 1 Full-art stained-glass Swamp 2 Traditional foil Swamp 1 Theme description card Ready to Charge 1 Ragefire Hellkite (Jumpstart Booster rare) 1 Random red rare or mythic rare 1 Electrostatic Infantry 1 Yavimaya Steelcrusher 1 Balduvian Berserker 1 Dragon Whelp 1 Coalition Warbrute 1 Molten Monstrosity 1 Flowstone Infusion 1 Twinferno 1 Jaya's Firenado 1 Furious Bellow 5 Mountain 1 Full-art stained-glass Mountain 2 Traditional foil Mountain 1 Theme description card Ready to Attack 1 Ragefire Hellkite (Jumpstart Booster rare) 1 Random red rare or mythic rare 1 Phoenix Chick 1 Electrostatic Infantry 1 Goblin Picker 1 Flowstone Kavu 1 Dragon Whelp 1 Coalition Warbrute 1 Hammerhand 1 Lightning Strike 1 Jaya's Firenado 1 Twinferno 5 Mountain 1 Full-art stained-glass Mountain 2 Traditional foil Mountain 1 Theme description card Beast Territory 1 Briar Hydra (Jumpstart Booster rare) 1 Random green rare or mythic rare 1 Floriferous Vinewall 1 Sunbathing Rootwalla 1 Deathbloom Gardener 1 Magnigoth Sentry 1 Territorial Maro 1 Linebreaker Baloth 1 Mossbeard Ancient 1 Bite Down 1 Broken Wings 1 Slimefoot's Survey 1 Wooded Ridgeline 1 Radiant Grove 1 Haunted Mire 1 Tangled Islet 1 Forest 1 Full-art stained-glass Forest 2 Traditional foil Forest 1 Theme description card Monster Territory 1 Briar Hydra (Jumpstart Booster rare) 1 Random green rare or mythic rare 1 Floriferous Vinewall 1 Sunbathing Rootwalla 1 Nishoba Brawler 1 The Weatherseed Treaty 1 Magnigoth Sentry 1 Territorial Maro 1 Yavimaya Sojourner 1 Gaea's Might 1 Slimefoot's Survey 1 Bite Down 1 Wooded Ridgeline 1 Radiant Grove 1 Haunted Mire 1 Tangled Islet 1 Forest 1 Full-art stained-glass Forest 2 Traditional foil Forest 1 Theme description card
This could have been a one-off nod to an old mechanic, something WotC occasionally does at mythic rarity
Rewards: 36x Wonder Hourglass, 12x Pack Hourglass, 1x Legendary Birds icon (below)
