Hello,
I've made a functional card script that turns just about any format into a Horde format.
You can even turn enemy encounters in Adventure mode into a Horde game if you have the card script on your library before encountering an enemy.
I wasn't sure on how to reach out to the devs without DMing them so I am posting this here and am welcoming people to give this a try if interested.
https://discord.com/channels/267367946135928833/1054520439927484496