The closest resemblance we have to this in card games is Magic: The Gatherings Commander format - though One Pieces leader mechanic is distinct from this
Heres a simplified guide: Modern Charizard cards: $10$200+ USD (ungraded), rising with condition and rarity

1 Exterminatus 1 Collective Effort 1 Deploy to the Front 1 Fell the Mighty 1 Hour of Reckoning 1 Launch the Fleet 1 Martial Coup Instant (6) 1 And They Shall Know No Fear 1 Deny the Witch 1 Entrapment Maneuver 1 Utter End 1 Swords to Plowshares 1 Mortify Artifact (14) 1 The Golden Throne 1 Inquisitorial Rosette 1 Knight Paladin 1 Reaver Titan 1 Thunderhawk Gunship 1 Everflowing Chalice 1 Mind Stone 1 Skullclamp 1 Sol Ring 1 Talisman of Dominance 1 Talisman of Hierarchy 1 Talisman of Progress 1 Arcane Signet 1 Commander's Sphere Enchantment (4) 1 Defenders of Humanity 1 Birth of the Imperium 1 The Flesh Is Weak 1 Reconnaissance Mission Land (37) 1 Choked Estuary 1 Darkwater Catacombs 1 Exotic Orchard 1 Port Town 1 Prairie Stream 1 Skycloud Expanse 1 Sunken Hollow 1 Arcane Sanctum 1 Ash Barrens 1 Memorial to Glory 1 Command Tower 1 Dismal Backwater 1 Evolving Wilds 1 Path of Ancestry 1 Scoured Barrens 1 Terramorphic Expanse 1 Tranquil Cove 5 Island 7 Swamp 8 Plains White (21) 1 Celestine, the Living Saint 1 Defenders of Humanity 1 For the Emperor

Then you can spend four mana, one Phyrexian white, to make a 1/1 aforementioned Mite token, so this is a mana sink in the later game or can let your Mites kills with normal damage quite quickly
Legendary is a supertype that can apply to many card types, including lands, artifacts, enchantments, and planeswalkers
A deck may contain any number of copies of CARDNAME