Most of the complexity is to handle a small number of cards that are essentially never used except to prompt rule puzzles. The rules have to be very complex to accommodate when these complex cards redouble their complexity by interacting with each other. Sadly, this doesn't work, because the game rules are complex enough to simulate a Turing machine, and as a result some board states are undecidable!

https://arxiv.org/abs/1904.09828