Released in their very own Secret Lair in October 2020, the Walking Dead cards came out before the Universes Beyond term was coined and was grandfathered in, becoming part of the product line retroactively
He dominated all of the formats he was legal for
Card Name Shadowheart, Dark Justiciar Mana Cost Type Legendary Creature Human Elf Cleric Rarity Rare rules Text , , Sacrifice another creature: Draw X cards, where X is that creature's power.Choose a Background (You can have a Background as a second commander.) P/T Set Number 392 Language Legal Formats Commander, Legacy, Vintage Not Legal Formats Alchemy, Brawl, Competitive Brawl, Historic, Modern, Pauper, Pioneer, Standard, Timeless Rulings (6/10/2022) Choose a Background is a variant of the partner ability
In this case, you'd be able to use them due to the casual nature of Commander