A few days ago, while messing around with ODST, I realized you could make inputs right after pausing, so I tried to see what all I could do with that information. It eventually snowballed into me realizing you could do something I'm calling "Revert Stacking" where you can pause and revert to the last checkpoint many times at once, or you can revert and restart multiple times at the same time, or revert/restart/and end the game all at once. While it was initially Coop only, I discovered a way to perform the glitch, albeit a little bit limited, in single player. There is no known way at the moment to perform this glitch in MCC.
It's worth noting that Halo 3 is really easy to crash with this glitch. If you revert and restart enough times at once, it'll black screen until you restart your console. This happens on the 360 and Backwards Compatibility versions. ODST doesn't seem to crash which is interesting.
I don't believe this glitch has any real use, but it's still neat that new random glitches are still being found.