Back when Arena was first announced, there was an interesting line in their write-up: https://magic.wizards.com/en/news/feature/everything-you-nee... >We've created an all-new Games Rules Engine (GRE) that uses sophisticated machine learning that can read any card we can dream up for Magic. That means the shackles are off for our industry-leading designers to build and create cards and in-depth gameplay around new me…
It's a parser + (de)compiler and rules engine which I'm trying to get to 100% coverage over all Standard/Modern/Vintage/Commander legal cards. About 23000 of them are partially supported, while 15k currently work in full (~3k more than what MTGA currently supports, IIRC). It also allows for P2P 4-way multiplayer which Arena unfortunately does not :/