And by that I mean "the game state produced a logical contradiction that couldn't be resolved just by the current rules" ?

The last one that comes to mind involved Splintering Wind (to create a token creature named Splinter), Clone (so that there would be a nontoken creature named Splinter), Mask of the Mimic (to search your library for a card matching that name and put it "into play"), and a Splinter card in your library (to be a card that has no business on the battlefield). The initial hack was to change the name of the token created by Splintering Wind, but eventually they added rules to flatly forbid instants and sorceries on the battlefield.