Man you know what's funny? This is obviously based on MTG, and the weeb community also doubles as a home for many MTG players. Most MTG players would be able to use those rules to show that obviously this situation makes no sense in the realm of MTG rules, even older rules. The issue is that the author is just loosely referencing the card formatting, symbols, stat alignments and general turn format but none of the comprehensive rules or judge rulings, and appears to have a different set of those for the story.
This causes dissonance between what the story says happens and what we expect to happen based on prior knowledge. The issue is that this manga's whole shtick is being ""MTG"" except isekai, but relying upon MTG to carry the story a REALLY long way (the author didn't have to create his/her own card game, explain the rules and mechanics as well as officiating a few different "what-if" rulings, he could just be like "it's MTG basically" and every MTG player knows how it works roughly) but then doesn't meld or define how the new world's rules will interact with the MTG rules.
This chapter basically started as a 2 "player" game, 1vs1 but then halfway through a third "player" joins immediately without consent to either "players". Like wtf? In MTG you can't just join a game that's explicitly 2 player, or even join a multiplayer game that's already in progress??? The rules just straight up don't accommodate that situation occurring at all, and I bet if someone tried to pull that shit anywhere, let alone the judge, EVERYONE would likely not be okay with it.
The problem is that this is a real, living world and not an isolated MTG game. This could happen at any time and it completely clashes with the rules of MTG. It could be more equivalent to say that this world is basically one HUGE multiplayer game of MTG except it's proximity based and the turns are taken basically at the same time as everyone else. Which has never happened in MTG ever as well, so the author should have clearly defined this upfront. I am hoping the author can use this for growth, so the MC can better plan for this as this clearly is not going to follow the expected rules of MTG, or any card game for that matter.
No matter how you slice it, MTG is way too established and too popular of a game to loosely reference or use without reader backlash and dissonance: either you use and follow all the rules of MTG, or don't use any of them. Being lukewarm and just using MTG as a convenient way of establishing the MC's isekai powers and explaining them to the audience without effort is really shallow, gatekeeping and bad writing.