From the study: https://arxiv.org/abs/1904.09828
> This paper completes the project started by Churchill [4] and continued by Churchill et al. [5] of embedding a universal Turing machine in Magic: The Gathering such that determining the outcome of the game is equivalent to determining the halting of the Turing machine. This is the first result showing that there exists a real-world game for which determining the winning strategy is non-computable, answering an open question of Demaine and Hearn [10] and Auger and Teytaud [1] in the positive. This result, combined with Rice’s Theorem [13], also answers an open problem from Esche [11] in the negative by showing that the equivalence of two strategies for playing Magic is undecidable.
> This result raises important foundational questions about the nature of a game itself. As we have already discussed, the leading formal theory of games holds that this construction is unreasonable, if not impossible, and so a reconsideration of those assumptions is called for. In section V-A we discuss additional foundational assumptions of Constraint Logic that Magic: The Gathering violates, and present our interpretation of the implications for a unified theory of games.