We haven't been to Blackthorn City yet for a reason -- it's due east of Mahogany Town, and even with the seventh badge in hand, you still can't leave the town towards the east (you'll be stopped from advancing automatically if you try)
Lost Leonin
the problem is thats not all that could be hiding below the depths of a Golos deck
Blindly Loyal Goblin is one of the more notable choices

Monsters 3 cards Mekk-Knight Blue Sky 3 Mekk-Knight Indigo Eclipse 3 Mekk-Knight Purple Nightfall 1 Mekk-Knight Green Horizon 1 Mekk-Knight Orange Sunset 1 Sheet Mekk-Knight Yellow Star 2 Mekk-Knight Red Moon 2 Mekk-Knight Girsu, the Orcust Mekk-Knight 1 Star Relic - "Star Cup 1 Star Relic - "Star Armor 2 Gameciel, the Sea Turtle Kaiju 3 copies Knightmare Corruptor Iblee 1 Star Relic - "Star Crown 1 Lava Golem Magic 1 Change of Heart 1 Harpie's Feather Duster 2 cards World Legacy Succession 1card Mind Control 1 World Legacy Scars 3 World Legacy's Memory 1 World Legacy Key 1 Lightning Storm Trap 2 cards World Legacy's Secret 1 World Legacy Whispers EX 1 Dingirsu, the Orcust of the Evening Star 1 copy Salamangreat Almiraj 1 Galatea, the Orcust Automaton 1 I:P Masquerena 1 copy Lib the World Key Blademaster 2 Mekk-Knight of the Morning Star 1 Mekk-Knight Spectrum Supreme 1 Mekk-Knight Crusadia Avramax 1 Mekk-Knight Knightmare Unicorn 1 Dingirsu, the Orcust of the Evening Star 1 Linguriboh 1 Ningirsu the World Chalice Warrior 1 copy Knightmare Cerberus 1 Knightmare Phoenix Knight of the World Deck Jack Knights Deck Jack Knights Deck 38N #Preconstructed Deck Item ID: 2147215597

Suddenly your opponent can't attack with him good creatures, or block with his good creatures, while you are free to send your happily into the red zone