The developer of Mesen has implemented a "run-ahead" lag reduction feature on the emulator, which unfortunately leaves us no choice but to remove the emulator from our allowed list effective immediately.

Runs already approved will not be removed. Any future submissions will be rejected and there are no pending runs in the queue.

https:/​/​www.​mesen.​ca/​docs/​configuration/​emulation.​html will show you this section:

Run Ahead: Run ahead allows the reduction of input lag by the number of frames specified. CPU requirements increase proportionally with the number of run ahead frames specified.

Run ahead is currently not compatible with movies or netplay - the movies and netplay menus will be disabled if runahead is turned on.
Note for speedrunners: Using features such as run ahead to reduce lag typically counts as cheating for the purposes of speed running.

If a run was already submitted with MESEN before this rule change, will it be removed?

Existing runs will stay, any future submissions will be rejected.