The first step is to ask the LLM to brainstorm 15 possible mechanics for the card
Its what is winning isnt necessarily a convincing argument on its own, but youd have to try really hard to get me away from registering a pile of basic Forests any time you cant fetch a basic land off of your opponents Ghost Quarter, Field of Ruin, or Path to Exile is enough of a disaster that I think you need a really good reason to play a second color right now, especially considering the basic Forests also help insulate you against the Blood Moons out of decks like Mardu Pyromancer
It's brokenly good
The funniest interaction I got in mind is playing it for 1 + 1 with Thalia, Guardian of Thraben on the board, and sweeping basically all the creatures from Human deck
I am definitely excited to see how these cards impact Commander and how my recommendations might influence your decks in particular
The abundance of creatures in Commander games means that Vanquish the Horde will often cost a paltry two-mana, most likely leaving its caster with plenty left over to take advantage of the empty, newly vanquished battlefield