Mayor's Residence is Entrance 0000, which is the default entrance of the game. There are various glitches which cause the game to default to loading entrance 0000.
Saving at the Hidden Owl Statue in West Clock Town will take you to Mayor's Residence when you reload the file.
Entering a grotto while it is culled will take you to Mayor's Residence.
If you enter certain grottos, then hover out of bounds to Alternate Exit to a global grotto you have not entered before, you will be taken to Mayor's Residence, and softlock.