LSV Breaks MTGO

There’s never a time where players can’t interact - just passing priority or putting triggered abilities on the stack are actions. And each time this could happen the game checks state based actions to see if someone has won. That said, if both players have no options or just pass (which is more pronounced online) then you can end up in inescapable loops that cause draws. A classic example is this Luis Scott-Vargas game: ▶ this video

> Regarding the oblivion ring loop, there's an example of it being used on MTGO, which doesn't end well (basically seems to crash the server and/or client): ▶ this video Oh wow, I should have realized that somebody would try it out online just to see what happens! I'm not surprised it ends up with some sort of clash; given that it's Turing complete, the game engine obviously can't detect whether a current state will end up halting or not... > And here's the paper on the latest turing machine construction in mtg: link Awesome, thanks! I'll definitely check that out

That rule is exactly where the the construction used becomes interesting: it's built in such a way so that if the turing machine halts, the player who set it up wins the game. If it doesn't, by the rule above, it's a draw. So it's fundamentally impossible to tell the result of an arbitrary setup (and in practice you could set it up such that it halts iff some unknown conjecture is true). Regarding the oblivion ring loop, there's an example of it being used on MTGO, which doesn't end well (basically seems to crash the server and/or client): ▶ this video And here's the paper on the latest turing machine construction in mtg: link

There's also the infamous video of (well-known professional player) Luis Scott-Vargas "breaking" MTGO by causing the game to wind up in a non-terminating loop of mandatory actions: ▶ this video For those who are confused, the card involved there is Oblivion Ring: link Its effect is that, when it comes into play, you choose a non-land card in play that gets exiled (removed from play) for as long as Oblivion Ring stays in play, then gets returned once Oblivion Ring leaves play. This game devolves into a situation where there are three Oblivion Rings and no other non-land cards, so: Ring 1 exiles Ring 2, which returns Ring 3, which exiles Ring 1, which returns Ring 2, which exiles Ring 3, which returns Ring 1, which exiles Ring 2, and so on to infinity. The rules state that when a loop like this occurs (which is not often in real play), the game is an automatic draw.